Rainy Mood is a good one.
Tetsuo Inoue has done some great stuff. If you're trying to read or study, it's not too distracting and it's good for just relaxing.
J.S. Epperson has a website with some great free tracks for focus and he has some hour-long tracks on Amazon that are only .99 cents. His music includes things like "binaural beats" which (allegedly) can help foster mental states conducive to concentration or sleep or whatever. I just like listening to it.
Edited by GungaDin - 4/7/13 at 1:34pm