My Dying Bride are pretty damn good, personally my two favourite albums of theirs are The Angel and the Dark River and Songs of Darkness, Words of Light most of the stuff is good though, just avoid 34.788%... Complete, and most of the recent stuff as they are getting more and more into more Gothic Metal areas with clean vocals and slightly more optimistic songs. haha.
Primordial, though they more on the Black/Folk side usually I thought their album To The Nameless Dead was very doomy (and fantastic.)
Are you into Doom metal for the sound or is the bleak atmosphere part of it too? because if so check out Lifelover, not strictly Doom metal, almost like Rock with Black/Doom influences but as I said, for bleak atmosphere they are pretty damn good.
My favourite Doom Metal band: Forest of Shadows I can't give opinions on their full lengths but their 2001 EP Where Dreams Turn to Dust is amazing.
Also, as the above poster mentioned, definitely check out Acid Bath all their stuff, though I think When the Kite string Pops is the best.