Honestly, I listen to Explosions in the Sky. If you haven't heard of them, I definitely recommend at least checking them out. While they are an actual band rather than a peaceful recording, their music is all instrumental, and it's so very soothing. I have horrible insomnia, but they can actually help with it more effectively than any other background music I've played.
Lemme know what you think about em(:
PS. Some starter songs:
-Birth and Death of a Day
-First Breath After Coman
-Your Hand in Mine
(but really, they're all pretty snazzy!)
I have always liked the sound of the heartbeat in the mothers womb. It's very relaxing and soothing. And you can find it in the Infant and Children's Department of just about all of the department stores.