A few that spring to mind that haven't been listed yet:
Zardoz - Beethoven's 7th Sym. (2nd movement)
Solaris (the original Tarkovsky version) - Bach's Chorale prelude for organ BWV 639. EDIT: Ah, I see Bruce has this one just a couple of posts up from mine!
Days of Heaven - Saint-Saens: The Aquarium.
Love and Death - Prokofiev: Lieutenant Kije suite.
Bread and Chocolate - Bizet's symphony.
It was through Stanley Kubrick's THE SHINING that I discovered the music of Krzysztof Penderecki, and I am grateful for that.
Me as well, which led me to meeting and chatting with the great composer himself several years later. His music is also heard to great effect in other movies such as The Exorcist and Shutter Island.
Prokofiev's LT. KIJE has been a lifelong love of mine which I first heard years before LOVE AND DEATH, when Ernie Kovacs used it in one of his ABC TV comedy specials. It was also used as the underscore in the 1958 Alec Guinness movie version of Joyce Cary's THE HORSE'S MOUTH.
As for the Sabre Dance, this was probably its most prominent presentation in a Hollywood film:
(Too bad the person who put this on Youtube cut out the amusing little bits of business before and after the performance, but at least the music itself is intact.)
