Some Non-Metal suggestions:

Lisa Gerrard (The Silver Tree) http://www.youtube.com/watch?v=Q6APV0An1Lg
Dead Can Dance (any album) http://www.youtube.com/watch?v=BNxa0odpCJU

Katatonia- Dissolving bonds i listen to this song every night... At 12:00pm

Deathspell omega - si monventvm Reqvires, Circvmspice

In general, the atmosphere of black metal is greatly augmented in dark atmospheres, but THE definitive "album to listen to in the dark" is without doubt Lurker Of Chalice's self-titled (Which Mr.Doctor already mentioned). There's something about that records that disturbs me every time. It's so deep and meaningful, while also being musically fascinating (Wrest employs a more ambient approach on LoC rather than his usual crazy dissonant riffs with Leviathan). Some other albums that would suit the dark atmosphere (Much less than LoC though):
Agruss - Morok
Deathspell Omega - Si Monumentum Requires, Circumspice
The Ruins Of Beverast - All Albums

Mostly anything Baroness does... Idk I enjoy their work alot in the dark