I wonder that nobody mentioned fuckin' CROWBAR! Ok they don't play the normal Doom, but Doomcore or Sludgecore! check out songs "December spawn", "Planets collide", "The Lasting Dose", "Empty room" and "Nothing". they had also covered Remember Tomorrow better than Opeth did. And LedZep's No quarter and Gary Whrights Dream Weaver.
Then they recorded some really downtaking experimental Songs: "To touch the hand of god" and "Odd Fellows Rest" where I really wonder about the vocals. You can cry to them!