Well I'm just starting to explore the true doom genre, but here are some doom related bands I ocasionally enjoy (not Ahab or MDB alike, except Shape of despair maybe, although less dark);
* NEUROSIS ( http://www.myspace.com/officialneurosis )
* ISIS ( http://www.myspace.com/sgnl05 )
* Shape Of Despair ( http://www.myspace.com/shapeofdespair )