I'm surprised no one mentioned American Beauty by Thomas Newman. I think the score had a lot to do with the film's success...I especially like the "SPEC-TA-CU-LAR" scene with the wonderful marimbas!
Here are a few of my favorites:
Wall-E - Thomas Newman
The Thin Red Line - Hans Zimmer
Tekkonkinkreet - Plaid (a must if you're a Plaid fan)
Moon - Clint Mansell
Memento - David Julyan