Jesu - Heart Ache. It's something in between shoegaze, drone and post-rock. Not very dark, but it has a nice atmosphere.
The Angelic Process - Weighing Souls With Sand. Dark and atmospheric, and really heavy. Like a more metal version of Jesu.
Om - God is Good. Rock, I guess. Distorted bass and tribal-ish drumming. Very relaxing, in an odd way.