My Top 10:
1. Crimson Tide (arguably the best soundtrack in the last 20 years)
2. TIE: American Beauty (great piano theme!) / Green Mile
4. Hunt for Red October
5. Gladiator (another great Zimmer work)
6. Jurassic Park 1 (2 is unimaginative at best, haven't listened to 3)
7. Star Wars, Shadows of the Empire. (Commissioned Horner work which is based off of a book by the same name. Very, very cool stuff.)
8. Final Fantasy (some good things on there; not the best but a solid soundtrack)
9. Star Wars Trilogy
10. Lord of The Rings (still too new for me to get a good handle on it, but it appears to be very good)

Honorable mention:
The Rock (clearly a case of too many cooks spoil the broth; they have a single theme which constitutes the majority of every track; not groundbreaking but interesting to listen to), Shawshank Redemption, Glory, Star Wars Phantom Menace (seems to be 'more of the same' from Williams).

Yeah, I'm a soundtrack geek.