kottke.org posts about Moon (movie)
Moon and Sunshine soundtracks Feb 26 2010
I don't know what took me so long, but I finally tracked down the soundtracks for both Moon and Sunshine...hiding in plain sight on iTunes. They are both great in their entirety. If you just want a taste, at least get Welcome to Lunar Industries from Moon and Sunshine (Adagio in D Minor) from Sunshine.
Update: Forgot to add that the Sunshine soundtrack is only available through iTunes and the Moon soundtrack is available in the US as an expensive import (and not on Amazon's mp3 site or anything like that) so your best bet is iTunes there as well.