Hey, I need opinions as soon as possible, because it involves eBay bidding. I'm looking for a Dream Theater-style tone from the pedal, and I'll be running it through a Traynor YCV-50 Blue. I know that the Fulldrive GT-500 isn't exactly a "high gain" pedal, but I got to try one today through a Marshall JCM and I really liked the sound of the distortion channel when I cranked it. I can't get my hands on a Damage Control Demonizer or a Blackstar Dist-x, could anybody give me a comparison on these? Thanks

I own a red GT500, and I love it for my purposes. I am using it with more of a vintage-style rig, and I think that this pedal was designed for vintage amps because it maintains my amp's tone very well despite being a distortion. I tried it in a store with a fairly cranked Twin Reverb, and it sounded like my Strat and the amp but with a ton of gain. If you're looking for something that covers up your tone a little more like more distortions do, then this is definitely not a good option.

I haven't tried the Demonizer or Distx, but I'm fairly familiar with the Crunch Box. The Crunch Box is a fantastic high-gain pedal if you want the classic Marshall tone out of just about any amp.
+1 to the Sansamp. The Demonizer is decent, but the Blackstar is utter sh*t. Noisy, muddy, and one-dimenional. The GT-500 is good, though. The Crunch Box isn't as high gain as the others.
I'm putting my GAS on hold
for a couple months in order to pimp my ride.

Don't judge me.
I love my Crunch Box, it sounds like a JCM800 on 'roids though, I dunno if that's what you're lookin' for.
I'm not really looking for a typical Marshall sound, so I'll probably pass on the Crunch Box. This makes my decision even harder because all of these reviews conflict completely with what Harmony Central says. I'll check out the GT-2, but I've always been wary of "modeling" pedals.
Ultimately, the only thing that really matters is what you think about the pedals and not what others tell you about them. Even that can change depending on who you're asking. The OCD and Crunch Box are almost universally loved here, but they're judged as subpar at best on other forums to other pedals and manufacturers. You also have the problem with most people gravitating to one of two judgments: they love it, or they hate it. Who can you really trust when that happens?

The best advice I can give you is either try them out with your gear before you buy them or buy from a place that will let you try a pedal for at least a few weeks and return it if you don't like it much. I went to my local store and a nearby Guitar Center twice each to try out pedals with my guitar and amp before I pulled the trigger; it was the best decision I could have made because I went for slightly more expensive pedals that ended up fitting very well with my tone.
Thanks for the advice, there are definitely really varied opinions depending on the forum. I can't actually find a place for me to try the Dist-x, Demonizer, GT-2, or Crunch Box, and I'd like to order it off of eBay which means that I can't return it. I'll keep trying to find them though.