I didn't really sleep last night and whenever I can't sleep I always think of this Eels song. I know it's off the Shrek 2 soundtrack, but it's still a really good song. I think this one is very appropriate. I don't know why this song has stuck with me so well. It's very simple: a basic drum beat, distorted electric piano, and what sounds like a music box. It works very in describing the feeling of sleeplessness.
Eels - I Need Some Sleep