Doing a complete search in these forums is quite overwhelming for finding out about distortion effects, hence this message. What I am looking for is a processor, either rackmount or possibly pedal type, where I can get an in depth, very heavy, and crushing distortion through a combo amp. I already have a Digitech Death Metal pedal and it is ok but it is lacking in some respects. My goal is to find something that will put me in the realm of Metallica's And Justice For All guitar sound, Pantera's sounds (towards the later albums) and perhaps Nile as well. My goal is not to dupe a particular band but to find something that is broad enough so that I have a good base from which to draw from. The amp that I am playing through is a Line 6 Spider 2, 75W, 1 12" speaker. The onboard distortion is ok but it lacks that special something. I would rather prefer to run clean and then just switch in/out my distortion. What can you suggest that will get me there? I would be interested in newer stuff as well as items that I might find on something like craigslist.

everyone is going to say just use the l6 as a firestarter. And recommend you buy a tube amp. But maybe check out the EHX metal muff
Music is the holy grail, sod wine water and the blood of jesus
I don't care if you run a $2,000 pedal through that Spider, you're not going to get a really good distorted tone out of it. You NEED a new amp.

How much do you think you can spend?
You're not gonna like this answer but.....You need a new amp, that spider is atrocious.
I don't give a shit if you listen to me or not
If you are looking for that ballsy kind of distortion, you need a tube amp. No matter what pedals or add-ons you have, there is nothing that can get to fill in for genuine tube sound.
Thanks for the comments. I am afraid that there will not be a new amp in the running at this time. I really cannot justify spending anymore money on a new amp. I bought this one as a used one. Maybe an alternative is to suggest something (pedal or whatever) that will do an admirable job as opposed to giving me the works. I should have been a bit more clearer about things but I would have never though that the line 6 spider 2 was "junk." I suppose one man's junk is another mans treasure huh. I think the amp sounds ok but I just wanted something a bit more.
It will never sound good, all I can suggest is saving every bit you can getting a suitable amp, otherwise all that hard earned money is a waste.
I don't give a shit if you listen to me or not
Lets take the amp out of the equation. What distortion effects would you suggest then? Do you think any of the modeler pedals out there are worthy? Others?
The spider isnt a terrible amp. Its just that for the price you could have gotten something ALOT better

Pedals dont usualy sound good on spiders but i guess if you got an EQ pedal and put your spider on the crunch setting it would be good for rock. It wont be ballsy but it wont be total **** either.

A bit of tweaking with an EQ pedal and you can get bearable tones out of crap (I got a good tone out of a metal zone )

A note about Line 6 amps : "You cant polish a turd."