Gah! I didn't know Clint Mansell did the Moon OST. Must acquire. I have been listening for The Fountain soundtrack (by Mansell) while programming - and I love it. I also just discovered he did the Pi soundtrack.
Other OST picks: Tron (and Tron Reconfigured) and Nick Cave / Warren Ellis soundtracks - particularly The Assassination of Jesse James by the Coward Robert Ford.
Both the Inception and Social Network soundtracks are excellent - check out the Batman Begins soundtrack if you get a chance - I like a lot of Hans Zimmers soundtracks and really dig that one too.
* Moon OST - Clint Mansell
* Donnie Darko OST - Mansell
* Inception OST - Hans Zimmer
* The Social Network OST - Reznor
* Simple Things - Zero 7
* Melody AM - Royskopp
* Abroreal - The Flashbulb (a lot of his stuff is good)