I have to say, there aren't a lot of songs that make me fall asleep. Most music keeps me awake because, for some reason, I have to listen to it. I can't study or read very well with music either, unless it is math and I'm listening to a rhythmical piece of classical music (weirdly enough). So this is a tough one.
I decided to choose one that relaxes me instead, which is also hard to find. I get excited and exhilarated over Mormon Tabernacle Choir and classical pieces that others find boring or soothing. Even Enya is exciting.
But this one is very peaceful, and I love it. "Abide With Me" is one of my many favorite hymns. I hope you enjoy it, too.