Every night I listen to Dream Theater, and somehow manage to fall asleep. They don't exactly make the most relaxing music but I just fucking love the band to bits and listen every time I can.
But there are two songs off the top of my head I remember as being very relaxing. Buckethead's "Too Many Humans" and "Baptism of Solitude". I'd youtube them for you but I'm capped and it takes too long for me to even load the youtube mainpage.