You can go on forever arguing who the heaviest band is, as different people have different definitions of heavy. Most would say that (insert brutal death metal band here) is the heaviest band, or some slower paced but bone crushing extreme metal band. Second most commonly, people will tell you that Black Sabbath is the heaviest band (this I really don't understand, but heavy means different things to different people). One CD that kinda fits both definitions of heavy (slow thick doom and extreme metal) is the new CD by Wreck of the Hesperus. The guitar sound is thick, the riffs are slow, dark and pounding, and the bass level is like that on Black Sabbath - Master of Reality. I myself can't even decide what single band I think is heaviest. I do think brutal death is heavy, since slam riffs are as heavy as fuck (but not necessarily good). Bands I think are among the heaviest include Infester, Suffocation, Asphyx (not brutal but heavy), Nile, Thornesbreed, Obituary (first two), Despondency, etc.