There are too many good composers and scores to list, so I'll just mention one of my all-time favourites.

I really like The Land Before Time by James Horner. Even if it borrows some things from classical composers, it manages to bring in originality as well, and it's quite complex composition-wise. There are many great and memorable themes that are hauntingly beautiful and brutal at times (e.g. the beautiful Whispering Winds theme and the theme for the Sharptooth). Orchestra and choir is used to a great effect, and the music really aids the film and helps to tell the narrative in a musical form. It also helps that the tracks are long, so it almost sounds like a symphony instead of a film score, but all in all it's a beautiful score that is still as stirring as it was back when I first listened to it.

Caraliz: If you like Clint Mansell's work, give Sahara a try. It's unlike anything he's composed before, because it relies more on the brute orchestral power than synth-laden stuff. It has many kickass and beautiful themes in it too, and it's an all-around upbeat adventure score.