Since atmospheric BM is one of the favorites here, and people love to talk about it, I'm sure you'll get a lot of good suggestions.
If you like Drudkh, definitely get all their albums. Forgotten Legends is probably their best work, and Autumn Aurora is very solid as well. The Swan Road is their weakest by far, so you've got some good stuff coming your way with the first two.
Hate Forest has the main guy in Drudkh, good stuff too. It's not as rich, though. More raw and minimal.
I've also really been enjoying Xasthur lately. It's a different feel that Drudkh, much darker, and without the folk melodies. Some people refer to it as suicidal BM, but I find it rather soothing, especially the recent Xasthur releases. Start with either the Xasthur/Leviathan, or the Xasthur/Nortt spilt. These works have rather good production, and like many Drudkh songs, are very easy to get lost in. Plus Leviathan and Nortt are really good too.