Generally, Stoner Doom is my home
InvokeTheDarkAge mentioned Sleep. I'm not going to lie to you, these guys were the pinnacle of all that has and ever will be.
Seriously, start with Sleep's Holy Mountain, listen to all the other bands, then come back and finish yourself of with Sleep's Dopesmoker. They are that good.
Otherwise, I'll add to the list:
Goatsnake
Graves At Sea
Warhorse
High On Fire
YOB
Ultraphallus (one of the lamest names ever, yeah? Not a bad band however)
Sons Of Otis
Negative Reaction
Mammatus
Of those Goatsnake and Warhorse are excellent, as is High On Fire.