Sort of a wierd request. I'm talking about dark ambient music that has a certain melody repeated, not just gloomy one-chord music. Something in the vein of Aäkon Këëtrëh or Burzum's last 2 albums preferably.
Its not really dark, but Brian Eno's "Music For Airports" is considered one of the first ambient albums ever and is pretty much entirely off looped melodies.