Aww hell yeah, dark jazz is great. I assume you know Bohren & der Club of Gore and Kilimanjaro Darkjazz Ensemble? (curious of any recommendations if you know more good stuff!)
I had expected that some of Badalamenti's stuff would have opened up since his death, like his score for Witch Hunt, but no luck. His stuff was sort of a wellspring, among others, which intermingled into that little creek we called darkjazz, for a while.
I originally got into it as a primary component of a long set of mixes for a particular mood, namely that I would have instrumentals (primarily darkjazz) buffering slow tempo "torchy" kinds of songs (Mel Torme, Julie London, Nat King Cole, Billie Holiday) and the "once every ninety minutes" track which was a little newer. The idea being that the darkjazz doesn't call too much attention to itself and keeps the mood going.