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.