I cannot fall asleep unless I have Zero Punctuation playing in the background. On Youtube they have started uploading hours-long compilation videos of his, and there are quite a few comments from other people saying it helps them sleep as well. A strange phenomenon.
When I was a kid, probably from ages 13-18 or so, I always fell asleep to a Harry Potter audiobook. I owned a copy of Half Blood Prince on CD (more accurately on 20 CDs) and I wouldn't bother changing out the disc (at least not that often), it was just some background noise to help me fall asleep.