Trist-
Hin-Fort
This was my first dive into ambient black metal. I was a little bit intimidated by this album, seeing as the first song spanned 60 minutes long. But boy, did those 60 minutes go by fast.
The song 'Hin' is one of the most complex, layered pieces of music I've ever heard. There is a constant, low frequency humming throughout the song, but melodies and little motifs are hidden underneath it. I've read that it's like "the music equivalent of staring into the void," and that is probably the best way to describe it.
Bjork-
Vespertine
Ol' Bj has released a lot of good material in my opinion, but this tops it for me. It's been described as "a winter sweater for your ears." Warm, fuzzy, and intimate, it fits the bill pretty well.
And yes, some of the lyrics can make an old lady blush.