2001: A Space Odyssey. "Also Sprach Zarathustra" might be hackneyed and mocked NOW, but remember ya heard it there first! If I'm in the proper mood for watching such an epic and overwhelming movie, the opening music is enough to send shivers down my spine (plus the Ligeti/Strauss later on is stunning).
Also, I enjoy the music for A Clockwork Orange and Scarface. And, yes, Pulp Fiction and The Godfather also have wicked music. And how about Requiem for a Dream?