Generally I can't sleep if I'm listening to music because I start listening too intently, and the music, not the sleeping, becomes my main priority.
However, recently I have been putting on Mogwai's 4 Satin EP at low volume when I go to bed. It's three tracks at 30 minutes, with the last song breaking down into a solid wave of distortion. By the time track three finishes I'm already out cold.
I used to listen to Kid A in bed a lot (I used to listen to it a lot full stop), and 'Treefingers' was great to sleep to (for obvious reasons I guess), but once 'Optimistic' started I would be jolted back into consciousness. Then I would fall asleep again at the end of 'Motion Picture Soundtrack' and the damn "secret track" bit would wake me up.
So maybe put 'Treefingers' on repeat for sleep?