Well, I don't know of a song that makes me fall asleep. I thought of a few lullabies, but in truth I'm not a big lullaby fan.
But, there is one that if my children were still small I might play for them at bedtime.
This song by Mindy Gledhill is like a lullaby and has a slight haunting quality to it which I love. And the fact that she has a great voice.
I had hoped to find a better clip - one that illustrated the words and meaning of the song more, but unfortunately wasn't able to.
You'll enjoy it anyway - it is truly a beautiful song.