I've used:
DOD - Death Metal -- good price, great for heavy stuff, didn't like the fact that I couldn't adjust the distortion level. It was like it was cranked on 10 and the knob was torn off
Marshall Jackhammer - more expensive, I love it though. It has a lot of differnet setting you can get out of it, from heavy metal, to blues, to light solo distortion.
Haven't tried the Boss pedal but they are usually pretty good. I'd recommend trying the Boss Metal Zone II I believe it is called.