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 )