Soundtrack to Twin Peaks.
No joke; it's pretty mellow and dreamy. When I had problems, I used to fall asleep to it on repeat.
The only caveat is there's that one musical vamp on "Into the Night," which would only bother me when I was falling asleep, not when I was actually asleep. I got used to it--it's a vocal track so I knew it was coming and it wasn't panic-inducing or anything--but you could just remove that from your playlist. It's also track 7, so after a while I'd be lying down, thinking "hey, don't forget there's that 'duh-duh-DUH-duh-duh' halfway through," but then I'd be asleep by the time it got to track 7.