I fall asleep to music every night, it's a must. The choice usually depends on how i'm feeling and how tired I am.
On the nights when it's harder to fall asleep to I have to put on mellower stuff and I know this is a Metal site but I fall asleep good to Counting Crows, Live, R.E.M., 3 Doors Down, Flaw but on the nights when I'm dead tired I can put on Unearth, Meshuggah, Chimaira, All that remains, mostly Albums that I know every song to so that when I wake up in the middle of the night I can still jam out.
I know the mellow stuffs alot different, but give it a shot, When Metals just not the mood of music I'm wanting those other bands definitely do the job.