Stoner Metal.

Electric Wizard - Dopethrone
Sleep - Jerusalem (Dopesmoker is the rerelease)

Two of the heaviest albums there are.
 
Yeah, but stoner typically refers to laid back bands, not oppressively heavy doom bands. Their newer stuff (esp. We Live) is definitely stoner in a lot of aspects, though.
 
Not really. Maybe Pyschedelic Rock if thats what you mean. Stoner Rock/Metal utilizes the extremely thick, downtuned guitar tone with lots of groove. Laid Back Metal is kind of an oxymoron of sorts, if I must say so myself.

Electric Wizard's Dopethrone is a Stoner Metal classic and is heavy as FUCK. Bongzilla isn't laid back whatsoever as well; on the contrary. You can't get much more Stoner Metal than that.