Six Feet Under - great theme. Echoes of it in "Deadwood" - I've not checked the composer.
Thomas Newman is composer of the "Six Feet Under" main title.
For "Deadwood", takes your choice (i.e., no main title credit given):
Series Original Music by
Shawn Thomas Odyssey (12 episodes, 2006)
Michael Brook (1 episode, 2004)
Reinhold Heil (unknown episodes)
Johnny Klimek (unknown episodes)