Discovered a new group lately in the Doom/Dark Jazz space. It's one of my favorite subgenres, being that it borrows so heavily from the cigarette smoke-veiled atmosphere of Angelo Badalamenti's jazz pieces from the Twin Peaks soundtrack. Senketsu No Night Club is the most recent addition to the relatively small group of artists within the space, borrowing some aspects from experimental Japanese film - as seen by the titles of some songs from their other album.
One of my favorite acts is Bohren & Der Club of Gore, who were one of the earlier bands to fully embrace the sound. If you liked Senketsu No Night Club above, I'd recommend listening to their album Sunset Mission. But they often explore the ends of what "Doom" and "Dark" mean in the context of the music and change their sound from album to album as they shift focus. My favorite to date is Dolores, which has an almost funeral-like quality without being overtly cheesy.
Most bands prefer to remain instrumental, but a few groups have vocalists that add significant texture. Dale Cooper Quartet & The Dictaphones (a quite on-the-nose reference) features both male and female vocalists, each fulfilling their own roles as either an aggressive croon or a whisper from a dream.
And of course, there's the more expansive work of the Killimanjaro Darkjazz Ensemble, who weave atypical instrument choices for the genre into their performances to give everything a more orchestrated feel.
Unfortunately, there's not much further to branch out from on this aesthetic alone, but every once in a while a new group shows up to keep the lights dimmed and the whiskey poured. Load up rainymood along with one of these if you really want to bring the mood down low!