The Umbersun by Elend. It's really disturbing with lots of choral arangements and screams/shrieks of absolute madness. It is probably the darkest piece of music I have ever heard.
Maybe not entire albums, but definitely moments in different albums... especially stuff like The Nefilim... that sends shivers down my spine... And some of the darker Opeth stuff can be quite atmospheric too...
Mayhem "De Mysteriis Dom Sathanas". Every time i listen to this album i feel really mad and anxious. Lately Crimson II of course for the melodics )
Cheers