Been slowly building an arsenal of pedals for my collection. I currently have:

Ibanez TS-9 Tube Screamer
BOSS DD-7 Digital Delay
BOSS BF-3 Flanger (I use it on the Rotary Flanger setting, which makes it sound somewhat Tremlo)
Digitech CF-7 Chorus Factory (LOTS of options and tweakability)
Korg Pitchblack Tuner
ProCo Turbo Rat (I (sadly) don't use it, too much hiss)

Any ideas on other (affordable) pedals I should check out? This thread is more for info than anything, I'm not made of $ but I'd like an idea of where to go from here.

-Major Bludd
An equaliser is always a great investment. On a budget, you can go with the Danelectro Fish n Chips, or if you have the cash an MXR 10-band is great.
Ibanez S520EX with Seymour Duncan Blackouts
ESP EC401FM with EMG81/60
VHT Deliverance 60
Laney VH100R
Marshall JCM900 1960B
Maxon OD808
Kind of hard to recommend pedals not knowing what kind of music you play or how much you want to spend, but based on what you currently have, here are a few that could help you expand your collection for relatively cheap.

Phaser: MXR Phase 90 or EHX Small Stone

Compressor: Visual Sound Route 66 or MXR Super Comp

EQ: MXR 10-band, a bit pricey, but worth the money.

Digitech Whammy: cool pedal, more expensive than others listed, and not really useful for all styles of music.

EHX Micro POG: a little more expensive, but a very cool octave pedal.

Wah: many different kinds here, I personally use a Dunlop. You can get them dirt cheap if you go used.
I play:

Motorhead, Led Zeppelin, Pink Floyd, Black Sabbath, AC/DC, NIN, Joy Division, Radiohead, Etc

Just to name a few.
what amp and guitar are you using, just to ask?
Ibanez S320 with Dimarzio Fred + Seymour Duncan 59-> Weeping Demon Wah -> Ibanez TS-7 -> Homemade iBoost x3 -> Keeley DS-1 -> Visual Sound H2O -> MXR Ten Band -> Traynor YCV20
Epiphone Sheraton II with an Epiphone Valve Jr.

Nothing too special, just a hobbyist on a budget.
definitely an eq pedal then, since the valve jr doesnt have eq built in.
if you can, you'd be best with a mxr ten band. though cheaper ones aren't bad either.
Ibanez S320 with Dimarzio Fred + Seymour Duncan 59-> Weeping Demon Wah -> Ibanez TS-7 -> Homemade iBoost x3 -> Keeley DS-1 -> Visual Sound H2O -> MXR Ten Band -> Traynor YCV20
Quote by Major Bludd
MXR Ten Band? I'll check it out...

Name some of these 'Cheaper' ones if you can.

MXR 10-bands are probably the best EQs out there...if you willing to go used you can get one for around $50 USD on ebay.
mxr 10 band eq and a classic crybaby is what you need
Member of the Schecter Hellraisers
Esp Ltd KH-603, Schecter c-1+ and Epiphone Les Pauls
Carvin amps, Sperzel Trim-Lok, Emg active pickups only, Tonepros bridges.
if you wanna go cheaper for an eq, the danelectro fish n chips, boss ge7, or mxr 6 band are all decent options.
Ibanez S320 with Dimarzio Fred + Seymour Duncan 59-> Weeping Demon Wah -> Ibanez TS-7 -> Homemade iBoost x3 -> Keeley DS-1 -> Visual Sound H2O -> MXR Ten Band -> Traynor YCV20
It seems like you have a good variety of good quality stuff, why don't you have a blast at building your own?
Get a wah and a reverb in there... or a pitch-shifter, but those are generally more expensive.
The Digiverb & Holy Grail are both good-priced reverbs that are pretty versatile.
Id suggest an EQ and a reverb. For the reverb, go for one of the Boss RVs, Digitech Hardwire, or Line 6 Verbzilla
Pitchblack - Fulltone Octafuzz - Hardwire OD - Blakemore Effects Deus Ex Machina - MXR Micro Chorus - Diamond Memory Lane Jr - EHX SMMH - Neunaber Wet
Question is do you need a certain pedal or do you just want more pedals for the hell of it? I only get pedals when it's something I need. This sounds like one of those things where you just want more and more and think it looks cool I guess. Why would you want to step on all of that? I hardly use anything only things that need to be used. Most bands I listen to are the same way too.

But the main point to this... If you have to ASK which pedal to get because you can't think of one. You probably don't need. it.
WOW! Lots of replies so far! Awesome...

I should explain that I'm not really out to buy another pedal just for the sake of buying another pedal, but rather to expand my arsenal of cool 'space rock' sounds. The first pedal I got (about a year ago) was the Boss BF-3 Flanger and though I love it, I kinda wish I looked a bit closer at the Phase Shifter as they demos I've seen on YouTube have impressed me greatly. Don't get me wrong, the Flanger is cool as hell - but there's only so much I can do with it. It seems to be more of an 'song intro' thing, or maybe I'm just overanalyzing...

I was looking at the MXR Phase 90 the other day, I have a question for those that use it - Is it noisy? (hiss, etc..) My BOSS pedals are very quiet and I like things that way, just wondering how the MXR pedals compare witht the BOSS by way of noise/hiss.

Wow, reading over this message I notice what a pure Newbie I sound like. That's probably because I am, I'm really just starting out and I need some direction.
Some cheaper eq's are the danelectro fish n chips and a boss 7-band.

MXR is a quality brand, I wouldn't be concerned with tons of hiss from their products

Maybe look into a fuzz as well
I was actually looking into a Fuzz pedal, yes. I tried the new BOSS one and it's cool, but WAY to expensive.

Not sure about the Big Muff Pi. I've heard some say it's fuzz, others say harsh distortion...