Okay, this list was originally posted by Dave_Mc (so he did 90% of the work here) and additional info got added by others from time to time. I made some minor updates with the help of some of the regulars in GG&A yesterday. Thanks to Dave for the original one and thanks everybody for their help!
Key: C = combo, H = head (if you buy a head, you have to factor in the price of a speaker cabinet into your budget too), H/C = available either as a head or a combo), USA = cheaper in USA (not a direct conversion), Euro = cheaper in Europe (not a direct conversion. In both these cases, I advise that you search for the price yourself. * = I’ve tried them (personal recommendation).
Anyway, here goes:
$0 - $150 (~£95, 110€)
First off, you probably WON'T get an amazing amp at this price range. However, if you’e lucky you’l be able to get a decent practice amp that will suffice until you’e able to get a “real” amp.
Lower Gain:
Vox Pathfinder* (1 channel with boost) (Euro, C): I have one of these. Nice (AC30ish) cleans, nice classic rock crunch, not so good higher gain- harsh, and no real sustain. It does a sort of Lenny Kravitz-esque sound with the gain above 2/3 like in "fly away" and "are you gonna go my way", if you're into that, very harsh and fuzzy. Good value.
High Gain:
Roland Cube 15/20/Roland Microcube (1 channel) (USA, C): I recommend saving for the Cube 30, since the Cube 15 and 20 have no (or very few) amp models, but you could do a lot worse for the price. The Microcube would be good for strictly practice purposes (it’s only 2W), but has built-in fx and amp models- really good for practice. In most cases, the Microcube is therefore better than the Cube 15/20, as they all are not loud enough for e.g. band use, but the Microcube is best for home use. In general, Cubes are also really compact (Thanks to jj1565 (Jenny) for this info)
Peavey Vypyr (USA, C): If you don’t have the cash for a Cube 30, but want amp modelling nevertheless, this is a good choice. Not so great for lower gain imo, but does metal well.
Washburn BD15 (according to gpderek09) (USA, C): Not great cleans, but for high gain on a (very cheap) budget, it rocks.
Ones to avoid:
Marshall MG (crappy cleans, worse overdrive, unreliable), Fender Front man (the 25R has nice cleans, but unreliable electronics, and muddy distortion), Behringer (poor quality), Ibanez TB and TBX (all around poor tone), Line 6 Spider III (sounds digital), anything priced too low (all those no-name ones!). (again, thanks to Jenny for the Fender and Behringer info here!)
$150 - $400 (~£95 - £250, 110€ - 285€)
Now you should be moving into quality practice amps- if you spend this amount of money, you shouldn't need to buy a better practice amp, ever. Unless you want something like a Cornford Carrera .
Lower Gain:
Epiphone Valve Junior/Special, Vox AC4 (both 1 channel) (USA, H/C). Both are especially nice when using an overdrive pedal. I wouldn’t recommend using the Valve Junior for clean tones unless you have a single coil guitar. It's best to get the latest version of the VJ (version 3), because some technical problems have been eliminated with this version. It's usually no prob when buying new, as pretty much all VJs in stores by now are the version 3, but if you get a used one, watch out.
Fender Champ 600 (1 channel) (USA, C): If you want Fender cleans at a low budget and tubes. Tiny speaker, not enough volume to play with a band, but it's small, portable and has nice cleans.
Mid Gain:
Vox Valvetronix VT15/VT30 (2/3 channel) (Euro, C): good range of tones - can get into metal territory too, but is supposed to excel at rock tones.
Blackheart Killer Ant BH1 (H) + Blackheart BH112 cabinet (USA): Good “British” rock tones, but only for home practice and recording, since it only has 1 watt of power. It’s nice to have a cab already when upgrading to a different head at some point.
Blackheart Little Giant BH5 (1 channel) (Euro, C): If the Killer Ant is too small for you. The Little Giant can even be used for band practice at full tilt, don’t expect clean tones from it at such volumes though.
Peavey Valveking Royal 8 (USA, C): Not as middy and "British" as a Valve Junior, but not as bright as a Champ 600 either - good if you need both, good cleans and nice drive.
Fender Vibro Champ XD/Super Champ XD (several channels, not footswitchable) (USA, C): Solid state preamp with analogue modelling, tube power amp with either 5w (Vibro) or 15w (Super) of power. Haven't tried them myself, but they are supposed to be very nice and have lots of good amp models of Fenders. Built in effects, too.
High Gain:
Roland Cube 30/60 (2 channel) (USA, C): Good high gain models, possibly slightly harsh cleans and rock tones. Uses boss non-latching footswitch (according to mnbaseball91)
Peavey Bandit (2 channel) (USA, C): Good range and quality of tones for a solid state amp. Not a modeller, though.
B52 AT112 (2 channel) (USA, C): No personal experience, but is supposed to be a good heavy rock and metal tube amp on a budget, in the US, anyway.
Blackstar HT-5 (2 channel) (USA, H/C): 5w tube amp for anything up to heavy rock. Great distortion for it’s price.
Ibanez Valbee (2 channel) (Euro, C): 5w like the Blackstar, but smaller, with a tiny 6.5” speaker and therefore does not have much low end. Not loud enough for band use, but a great rock amp for home use.
Ones to avoid:
Marshall MG (as before- but add in “crappy fx” too!), Line 6 Spider III (sounds digital).
$400 - $800 (~£250 - £500, 285€ - 570€)
At this price, IMO, you should be looking at smaller all-tube/valve combos (around 30 watts) or some of the better modellers. I’d recommend tube, but if you need super high gain, a modeller may be the way to go- although, remember, you can always boost an overdriven tube amp with an overdrive pedal! Another thing to remember is, dependent on type of power amp tube, that tube is 2-3 times louder than the equivalent solid state amp- i.e. 40 tube watts = approx. 100 solid state watts. See D man’s excellent amp post for more info! Also, another thing to note is that you can get solid state amps in this price range (Fenders, Marshalls etc.), but tube is normally the way to go, unless you’re going for a modeller (thanks to Jenny again, for the second half of this paragraph).
First, the all-tube choices:
Lower Gain:
Laney VC15 (by Gabel) - Nice clean, fantastic vintage tones, everything from Keith Richards almost up to Tony Iommi. Awesome small classic rock amp. Sound is close to Vox and Orange.
Laney VC30 (2 channel) (Euro, C): Vox AC-30ish in tones (according to power freak)
Fender blues junior/pro junior (1 channel) (USA, C): excellent blues and clean tones.
Peavey Delta blues (2 channel) (USA, C): Like the Peavey Classic 30 (see mid-gain section), but with tremolo and more bass. (thanks to Gabel for this one)
Mid Gain:
Laney LC15/LC30 (2 channel) (Euro, C): good cleans, good rock crunch. Great value in the UK.
Peavey Classic 30 (2 channel) (USA, H/C): Fender Bassman sound character. Great cleans, nice overdrive, in the lower section of Mid- gain spectrum. (thanks to gabel for this one)
Randall RG50TC (2 channel with boost) (USA, C): good crunch tones, and good value (this is a 50 watter!)
Peavey Valveking (2 channel) (USA, H/C): for an all-tube amp on a budget!
Traynor YCV 20 (2 channel with boost) (USA, C): smaller brother of the YCV40 (thanks to Jenny for this one!)
Traynor YCV40/50 (2 channel with boost) (USA, C): get the 40 for American/Fender-y tones (6L6 tubes), or the 50 for more British tones (EL-34 valves). Has better overdrive than the Fenders (according to Jenny!)
Peavey Windsor (1 channel) (USA, H): Haven’t tried it myself, but other UGers recommend it frequently. It’s basically a copy of the legendary Marshall JCM800, but a lot cheaper. 100 watts of nice distorted tone, but forget about cleans.
High gain:
Ashdown Fallen Angel 40 combo (2 channel with boost) (Euro, H/C): probably as close as you’re going to get to all-tube high gain at this price.
B52 AT100 (3 channel) (USA, H): I have no experience with this, since there aren’t even any distributors in the UK, but they’re meant to be good value if you live in the USA.
Bugera (various models): Clones of high gain Peavey amps. Great sound for cheap but early versions were unreliable. They are supposed to be more reliable by now, but I guarantee nothing! Still, good sounding, great value amps.
Now the better modellers:
Vox Valvetronix VT50, VT100 (several channels) (Euro, C): Versatile amps for band practice and gigging on a budget. All around nice amp modelling and effects, but if you don’t need the versatility, an equally priced tube amp is probably better.
Line 6 Flextone III (several channels) (USA, H/C): Better and more versatile version of a Spider.
Ones to avoid:
Bigger Marshall MG's (still crap, just louder!), Marshall AVT (nowhere near as bad as the MG's, but over-priced, and with some fatal tone/feel flaws), Line 6 Spiders (still digital-sounding, just louder!)
$800 – 1500$ (~£500 - £940, 570€ - 1070€)
IMO, here you should be looking at a semi-pro to pro level all-valve/tube amp. You may upgrade to a boutique amp for the ultimate tone, but (unless you have no room, or want to claw back some money) you should have no major reason to sell an amp in this price range if you decide later to upgrade.
Lower Gain:
Fender Hot Rod* (various models) (2/3 channel) (USA, C): Great cleans and blues tones. Can do rock too (according to Jenny!)
Mid Gain:
Vox AC30CC* (2 channel non-switch able) (Euro, H/C): great sparkly cleans, up to classic rock overdrive. At the lower end of the mid-gain spectrum.
Marshall TSL* (3 channel) (Euro, H/C): despite what anyone says, if you don't need a fender-y clean, or an uber-saturated metalcore tone, (assuming you like the Marshall tone) this is a great amp. It’s dear in the USA though. Also tighter sounding than the DSL, more versatile, and more equipped for metal (again, according to power freak).
Marshall DSL50/100 (2 channel) (Euro, H): Lower gain version of the TSL, with 2 channels instead of 3.
Marshall DSL401* (2 channel) (Euro, C): some people complain about Marshall’s price and tone, but if you want the marshall tone, this is about the cheapest way to get a half-decent all-tube approximation. And with a speaker swap, can contend with amps that cost more (e.g. traynor) (according to power freak)
Laney TT* (3 channel) (Euro, H/C): Fender-y (and jazzy!) cleans, good rock crunch, edging into higher gain territory too!
Orange Rocker 30 (2 channel) (Euro, H/C): Little brother to the 50 (I’ve tried) and 100 watt versions, should have great warm cleans, and a distinctive, warm overdrive- and has more gain than you'd think! (for USA people, www.humbuckermusic.com (thanks to mnbaseball91)) Quite dark sounding (according to power freak)
Hughes & Kettner Statesman Quad EL84 (2 channel) (Euro, C): 40 watts and a vintage sound and look. Does everything up to ‘80s rock. Great if you want a Marshall-y crunch and Fender-y cleans (well, sort of) in one amp. It’s technically a hybrid (the preamp is partially solid state), but it is easily as good as comparably priced all-tube amps.
High Gain:
Laney GH (1 channel with boost)/VH* (2 channel with dual boosts) heads (Euro, C): Fender-y cleans, Good crunch, aggressive high gain tones!
Engl Screamer (4 channel)*/Thunder (3 channel) (Euro, H/C): not quite as awesome as the dearer Engls, but if you want a high gain amp with versatility on a budget (kind of!), this is where it’s at. Fender-y cleans, Marshall-y crunch, insane high gain! Screamer gives a smoother tone than some of the higher gain amps (according to power freak) (thunder probably too, but I haven't tried it).
Cornford Harlequin (1 channel) (Euro, C): A 6W practice amp, but what tone! Cornford's “Sig tone” is that “growly bark” that you hear some aggressive blues guys getting (Power freak).
Peavey XXX (3 channel)/6505 (+)*(3 channel) (USA, H/C): struggling to make it into this price range in the UK, but easily makes it in the USA. XXX is brighter, with better cleans, and is probably more versatile, while the 6505 (+) has an intense, dark, modern metal high gain tone, and good crunch- but pathetic cleans.
Carvin MTS (2 channel) (USA, H/C): I haven’t tried it, but, as the B52, meant to be great value.
Ones to avoid:
once you get to this price range, there's nothing really to avoid- APART FROM SOLID STATE HALF STACKS AND FULL STACKS! Just don't do it. Please.
$1500 - $2500 (~£940 - £1570, 1070€ - 1800€)
At this price you’re into pro-level kit. You should be able to get amps that the pros use, and as long as you don’t want a boutique or Super-Amp, you should be able to get near enough exactly what you want.
Lower Gain:
Fender Reissues (Bassman, Twin, etc.) (1 or 2 channels) (USA, C): Great cleans and bluesy overdrive.
Dr. Z Prescription (and Prescription Extra Strength): A straight forward, vintage-style amp that's the dream of any bues and classic rock efficionado. (thanks to zavorash for this one!)
Mid Gain:
Vox AC30CC (with alnico blue speakers) (Euro, H/C): better speaker version of the Vox AC30CC mentioned above. Some people don't like the alnico speakers. They are a bit “flubby” and can lose definition (power freak).
Marshall Reissues (various models) (single channel) (Euro, H/C): more authentic (but less versatile) renditions of the Marshall tone.
Orange Rockerverb 50*/100 (2 channel) (Euro, H/C): As the Rocker 30, but more options.
Koch Multitone* (2 channel with boost) (Euro, H/C): Fender-y cleans (with footswitch-able gain boost for sweet blues tones) coupled with a hot rodded Marshall overdrive channel- excellent amp! The medium channel is smoother and the amp as a whole is basically described as a souped up Mesa/Boogie Mark (power freak).
Hiwatt all-valve models (single channel) (Euro, H/C): Haven’t tried them, but they’re supposed to be good for The Who and Pink Floyd tones. They are hard to get great tones out of them, for experienced players only!
THD Univalve/Bivalve/ Flexi 50 (single channel) (USA, H): Switch tubes at will, and great Marshall tones. Built-in hotplate attenuator in some models, too! Excellent recording amps. (this whole next bit thanks to power freak!) With Univalve be careful as there aren’t phase cancellations (technical gubbins!) which causes the tone to be a bit brighter than you’d expect. The Bi sounds “bigger” but the Flexi is a whole different beast!
Rivera (USA, H/C): various models and gain levels. Great choice for a range of tones, tend to have one channel which is "American-voiced", and one which is "British-voiced". I haven't tried them, unfortunately.
Framus Ruby Riot I/Ruby Riot II (2 channel) (Euro, C): 30w 2x12” combo with two different speakers (nice for recording). Incredibly warm and full cleans, like a Vox AC30 but less jangly and with better low end definition. Very warm, vintage-y crunch tones that are great for blues and classic rock, but it sounds a bit stiff right out of the box (factory biasing is pretty cold). The Ruby I has a lot of gain on tap, the Ruby II has less gain (which suits it better, imo) and a very nice tremolo effect built in. Imo, this is the best amp Framus makes and can compete with many boutique amps.
Framus CB (2 channel) (Euro, H): Head version of the Ruby Riot I.
Hughes&Kettner Statesman Dual EL34 (2 channel) (Euro, H): Much like the Statesman EL84, but with a different power amp. Haven’t tried it myself, but reports from friends and clips indicate that it sounds roughly the same.
High Gain:
Engl Powerball* (4 channel)/Savage (4 channel) (Euro, H): Fender-y cleans, Marshall-y crunch, hear-to-believe ultra high gain tones! Extremely versatile amps. Go Powerball if you play mostly metal, Savage if you play mostly hard rock but need metal tones as well.
Engl Ritchie Blackmore Signature (2 channel, each with 2 gain settings) (Euro, H): Like a hot-rodded Marshall with American-y cleans. Designed with rock in mind, but can do metal with the right guitar. Very very responsive, “ballsy” sound, and ridiculously loud (even for a 100w head), but sounds great at low volumes as well. Good value in Europe!
Mesa F30*/50 (2 channel) (USA, C): dark, intense high gain tones, good rock tones, decent cleans (still sound a little over-compressed to me though). Versatile workhorse.
Framus Cobra /Dragon (3 channel) (Euro, H): Tight high gain tones, great cleans. Versatile (from what I hear). The Cobra is aimed at metal and sounds extremely agressive, while the Dragon is all about versatility and is very articulate, even in high gain mode. Both have surprisingly nice cleans for high gain amps.
Cornford MK 50 (1 channel with boost) (Euro, H): That singing lead tone again! Look out for the twin channel MK50 2 that's meant to be coming out soon, it's promising to be sweet!
Cornford Carrerra (1 channel) (Euro, C): a 6 W practice amp again, but it’s self-biasing, and you can switch out pre- and power-amp tubes at will, while it’s on standby! And it’ll have that Cornford tone again.
Genz Benz El Diablo: (high gain, second highest price range) A versatile monster with an emphasis on heavier playing, but that still packs a surprisingly good clean and crunch. (Thanks to Zavorash for this one)
Hughes & Kettner Trilogy (3 channel) (Euro, H): The TriAmp’s little brother. Very versatile, a bit bright though, so possibly not for everyone. Good choice if a TriAmp or other 3- or 4-channel amps are too pricey.
Ones to avoid:
again, at this price range, you shouldn't get crap. The only thing to watch out for is to make sure the amp you get suits your style of playing. If you only play metal core, don't get a Fender, for example.
$2500+ (~£1570, 1800€)
Now you're talking! The world’s your oyster! Super amp that does every tone well, or a boutique hand-made amp that does one tone sublimely? the choice is yours. I’m not even going to bother listing them, because there are so many good ones. If you’ve got this much to spend the amp better be special! And if an amp at this price doesn’t do what you want it to do it offers worse value than an MG/Spider hybrid! One thing I must say though- at this price there are many boutique manufacturers. They may not have a big name, but avoid thinking outside the box at your peril! There are more good amps than Marshall and Mesa at this price range! And please make a thread in GG&A if you have this much cash! It makes a welcome change from recommending Vox Valvetronix amps.
/ my profile 
