Acid Bath is the best sludge band ever IMO, Golgotha too obviously, Soilent Green is fantastic, A Deleted Symphony for the Beaten Down being my favorite album. Baroness is the best for progressive sludge, kylesa is pretty awesome too. And I also enjoy Mastodon, bash me if you must. Leviathan kicks my ass daily
Southern Sludge is the best. Eyehategod, Iron Monkey, Weedeater (And all affiliated projects)... There's something just so awesome about it. Downright frightening.