I picked up an Aphex Punch Factory optical compressor a few weeks ago as a last ditch effort to find a good comp. I guess it's marketed for bass, but the instructions refer to both bass and guitar. It's extremely transparent and smooth sounding, no noise and has a built in DI out which can also run the comp on phantom power if needed. It's fast as hell, but doesn't kill the attack. The release seems to be a happy medium. Keeps the note going a while longer, but not so long that all you're left with is hiss by the end of things. Very usable. So far I'm really liking it for solos and clean stuff. I got it used for less than I'd have spent doing up a clone of one of the more popular comps.