Many of the better soundtracks have already been listed, so I'll just mention a few I like that could be overlooked:
1. "I Want To Live" -- jazz soundtrack by Gerry Mulligan for the movie starring Susan Hayward
2. "Chariots of Fire", with music by Vangelis
3. "'Round Midnight", jazz soundtrack by Dexter Gordon and others jazz greats
4. "Star Wars", soundtrack written by John Williams
5. A personal and sentimental favorite of mine: soundtrack from a 1957-58 Cinerama movie called "Windjammer". A variety of music, mostly vocal, with a strong Caribbean flavor.