I fall asleep every night whilst listening to my iPod, it's always lying next to my pillow and sometimes in the morning, when I wake up, the earphones are still in my ear (though the music isn't playing all night, of course)
To fall asleep I prefer listening to calm, slow songs, like Paolo Nutini's, Amy Winehouse's or Pete Doherty's acoustic recordings. Or The Strokes, I think Julian Casablancas has a very smooth and sedating voice.
More often than not it takes less than 3 songs and I am asleep.

billy holiday is the best thing to go to sleep to. ..take all of meee...

I only like it if I'm sleeping with somebody and they pick the music. Because it's fun to put up with people's shit when you like them.

And sometimes when I've just washed my sheets, it seems like a good idea to start listening to Underworld, Air, The Orb etc as I drift off to sleep. Like it will purify my life or something retarded like that. But it never works out that way because I just get annoyed after a song or two and shut it off.

i can fall asleep listening to ANYTHING. one of my favorite cds to listen to is Evan Dando's solo cd. its so mellow and soothing, but i usually only get thru the first 2 songs before im asleep

lately Brian Eno, Boards of Canada, Air, & Joanna newsom is who i fall asleep to.

I got this for christmas and its brilliant, has a sleep option where the music fades in volume and everything!