Acid Bath is good.
if you like them check out Agents Of Oblivion and Deadboy And The Elephantmen. they're both really different from AB but worth checking out (they Dax's, the singer, bands after AB broke up).
i got into AB first and then found out about his other bands and like them just as much (if not more).
i'm drawing a blank on any other sludge bands right now though (except for stuff that's been mentioned already).