I agree on Johnny Cash. And I dunno, maybe I'm off base... but my thoughts would be Nick Cave and Fields of the Nephilim.
Thanks for the Pine Box Boys link - I quite like throat singing and don't find it in much that isn't World music.
Edit: Wait. This might be too country and not dark enough, but try the song
Swamp Witch.
Also finding a lot of
hits for "dark alt country" with actual band lists. One of them is
Sons of Perdition.