Ambient music usually works best for me. It provides comfortable background ambience I can sync my rhythms to without my mind getting engaged with it. I have albums by Thom Brennan, Steve Roach, Robert Rich, and some others on my MP3 player, which I keep plugged into Sony SRS-P7 speakers beside my pillow at night. These require no additional electricity, and they can be placed nearby my head, so that they are loud enough for me without being too loud for people in other rooms. New age music and classical music sometimes work too, but these often engage my mind more.
Everyone seems to have a different type of music that helps them relax and fall asleep. I find that acoustic covers of songs I know tend to help me best. I have a bad habit of doing most of my thinking when I'm in bed, so listening along to calm versions of songs I know allows me to get my mind off the world when I need to sleep. Here's a link to my covers playlist:
Mostly I listen to audiobooks ;D But when it comes to music for falling asleep I can recommend Brian Eno. Particularly his >15min tunes are providing enough time to focus on just one track while heading towards dreamland. And arriving there before a new setting of sounds kicks in, grants just a very smooth transition.