Michael Nyman's score (the whole thing) for Gattaca is one of my favorites. Not only is it really good in its own right, it also complements the movie really well. It's a classy score for a classy hard scifi flick,
I love Clint Mansell. His scores for Requiem For A Dream, The Fountain, and Moon are all spectacular.
I adore the scores of Thomas Newman. American Beaty, Road to Perdition, hell even Finding Nemo, are all great. Some pieces from different movies sound a bit samey, I guess, but this is a problem I have with a lot of composers. I just learn their sound after a while.
Dario Marianelli's score for V For Vendetta (all of it) was pretty epic. It's a shame he hasn't done more work for big bigger movies.
I could go on forever.