There's a couple of soundtracks that have always been really good for laying me out and they are the Silent Hill 2 and Silent Hill 3 soundtracks. I picked all the ambient tracks off the albums and MY GOD they're just so entrancing to go to sleep to.
I usually leave a select large group of songs that I have off all four soundtracks and loop them, which would explain why
I have so many plays of Akira Yamaoka tracks on my Last.fm profile. Don't get me wrong... He's a great composer but I really don't listen to him THAT much for me to say "Yeah... That guy deserves 900 plays of ambient noise in my head".
Jam it back in, in the dark.