I've been gettin really into Doom/Sludge lately however admittedly Im still somewhat new to it, and dont know that many bands... However I do like

Pelican (fucking love them)
High On Fire (love them as well)
Mastodon (not sure if they fit into doom, but they fucking rock regardless)
Isis
Jesu
Sleep is pretty sweet from the little of what I've heard, I should get some of their stuff since I like High On Fire so much, and it is Matt Pike's former band is it not?
Boris was pretty cool from the little of what I've heard been meaning to pick up Amplifier Worship
Electric Wizard I've been hearing a lot about and have been told I'd love them
Sunn O))) Ive listened to a little of, different but pretty cool
Khanate Ive been meaning to look into as I kinda like the stuff on the Hydra Head label