Oooh, I LOVE this topic!
Well, my favorite composer is James Newton Howard, and the great curse with him is that his best scores tend to be for unremarkable movies, so they rarely get their due. My fave JNH scores are probably:
-Restoration - GORGEOUS music. Gets used in trailers quite often.
-King Kong 2005 (didn't like the movie but the score was especially impressive considering he only had 6 weeks to write/arrange/record it since he was replacing Howard Shore at the last minute)
-Signs
-Snow Falling On Cedars
-Treasure Planet
-Peter Pan (I listen to the Fairy Dance from this all the time)
-The Dark Knight - I think he only did the Two-Face stuff from this (and of course the return of his sentimental theme from Batman Begins), but it was great.
Other, non-JNH scores I love:
Hans Zimmer - The Thin Red Line, Gladiator, and The Lion King
John Williams - E.T., Raiders of the Lost Ark, and Harry Potter and the Prisoner of Azkaban
Dario Marianelli - Pride & Prejudice and Atonement
Michael Giacchino - The Incredibles, Ratatouille, and Lost (TV show)
Howard Shore - The Lord of the Rings: The Two Towers
Clint Mansell - The Fountain
All that said, my #1 absolute favorite score that I listen to most and never get tired of is Bear McCreary's work on Battlestar Galactica. Yeah, a TV show, but that stuff is just plain brilliant, breathtaking, etc. And that body of work is easily the most impressive music EVER produced for a TV series, and for my money is equal to anything to ever come out of the movies. I can't believe it never got recognized at the Emmys, but then again, the same goes for most aspects of that show.
I mean, they gave one to Legend of The Seeker and never even nominated this:
That I'll never understand, and I didn't even include my favorite tracks in that bunch.