Although I agree that peaceful and relaxing are usually the same thing, I've found that the music (VGM that is) that relaxes me or puts me to sleep the best is the stuff I like the most. While that usually isn't "Palace of Destruction"-esque rock hard tracks (I like it but probably it wouldn't lull me to sleep), it doesn't have to be all piano and strings either. Lots of beat-y soundtracks have relaxed me- take Eco Quest 1's soundtrack, Sonic CD USA or Pitfall: The Mayan Adventure for example. Of course, if it's too beat-y and you like it too much, you might bop around in your bed all night. But only you as the listener can know what's right for you
Good music that you enjoy- that's my recommendation for 'best VGM to fall asleep to'.
- Spike
Jam it back in, in the dark.