Well, I can't pick just ~one~ favorite, so here is my list, in no particular order...
The Empire Strikes Back (John Williams)
Dances With Wolves (John Barry)
Lord of the Rings (Howard Shore)
To Kill a Mockingbird (Elmer Bernstein)
E.T. (John Williams)
Ben-Hur (Miklos Rosza)
Vertigo (Bernard Herrmann)
Batman (Danny Elfman)
The Magnificent Seven (Elmer Bernstein)
The Good, The Bad and The Ugly (Ennio Morricone)
Braveheart (James Horner)
The Man in the Moon (James Newton Howard)
First Blood (Jerry Goldsmith)
Raiders of the Lost Ark (John Williams)
On Her Majesty's Secret Service (John Barry)
A.I. (John Williams)
Close Encounters of the Third Kind (John Williams)
Superman (John Williams)
Casablanca (Max Steiner)
Kundun (Philip Glass)
Crouching Tiger, Hidden Dragon (Tan Dun0
The Shawshank Redemption (Thomas Newman)
Edward Scissorhands (Danny Elfman)
Saturday Night Fever - lol - Flame Away!
Phillip Kaufman's two movies "The Unbearable Lightness of Being" and "Henry and June."