Heh, I always like this topic. I own a lot of movie soundtracks, and what I've done is rip the best songs from them to mp3, put all the mp3s on a CD (well, two now; I've got too many) so I can throw the CD into the DVD player in the room where we're playing and have enough music to last for hours. I usually put it on shuffle--I don't worry too much about matching specific tracks to specific scenes in the game or anything like that. That's too much trouble.
I have selections from all of the following soundtracks, and probably several more that I'm forgetting:
Stargate
The Mummy
The Mummy Returns
Van Helsing
Crouching Tiger, Hidden Dragon
Troy
Gladiator
Conan the Barbarian
Starship Troopers
The Last Samurai
Last of the Mohicans
Signs
Harry Potter and the Sorcerer's Stone
Harry Potter and the Chamber of Secrets
The Fellowship of the Ring
The Two Towers
The Return of the King
Patriot Games
End of Days
Sleepy Hollow
Aliens
Hook
Raiders of the Lost Ark
Braveheart
Bram Stoker's Dracula
Sum of All Fears
Minority Report
Batman Begins
Hunt for the Red October
Heroes of Might and Magic III
Heroes of Might and Magic IV
As you can probably imagine, my campaigns tend to develop a darker, almost horror vibe.