I think it would be a grave mistake not to mention Ennio Morricone in this thread. This guy's Sergio Leone "Spaghetti Western" soundtracks helped revolutionize the way music and sound were used in films.

His soundtrack work includes:

- A Fistful Of Dollars
- For A Few Dollars More
- The Good, The Bad, and the Ugly
- Once Upon A Time In The West
- Once Upon A Time In America
- Days Of Heaven
- The Thing
- The Untouchables

Not bad, eh?