Most of teh good stuff has been mentioned (on this page anyway, i didn't read the whole thread as its really old)
i would add Evoken: quietus(fav) and embrace the emptiness.
all Skepticism (fav)
funeral: tragedies.
all Unholy, esp gracefallen and the second ring of power
Shape of despair (fav)
Dolorain: i prefer when all the laughter is gone, but the self titled is good too.
these are mostly funeral doom bands, as oposed to the more traditonal (candlemass) and doom/death (my dying bride. all is good though.
My dying bride is one of my favorite bands.
St. Vitus hit most of the rest...I'd add icon to the paradise lost list, and as the flower withers and the dreadful hours tot he my dying bride list. also, everything from novembers doom is good, though the knowing and the newest one being the best.
also,add the karelian isthmus to the amorphis list (though i love all their albums, the first two are the doomiest).
He listed morigion, but i can't stress enough how amazing solinari is. mandatory.
I would add primordial too, esp spirit the earth aflame.
High on Fire is a good band, though they are more in the stoner/doom field. a bit darker than a lot of those bands thogh.
i dont recommend khanate. can't stand em.
warhorse is cool, as is electric wizard (definatley not slow doom, evoken, funeral, skepticism own that title), though not my favorite shit.
of course you must own candlemass epicus...and you must get cathedral forest of equilibrium. that be some slow shit.
Insanity reigns supreme is good doomdeath though not very original. talented band. in 10 years they've released one album
Dusk is another favorite of mine, they recently issued both their eps on one cd. track it down if you can.
i've not see Disembowelment listed. mandatory.
Im gonna stop there. sorry if i repeated anythign....and this was totally as i thought of it, thats why its a messy post.