Here are my choices for the best movie theme music of all-time.
1. The Godfather
2. The Exorcist
5. (tie) The Last of the Mohicans (tie) Rocky
Honorable mention to The Sting.
Other movies have had some great songs but when you hear these instrumentals - your brain automatically thinks of the movie.
Interesting to note that all of the movies except Last of the Mohicans (1992) were from the 1970's. Also all the songs except The Exorcist (Tubular Bells) and The Sting (The Entertainer) were original scores. Do movies these days need hit songs associated with them to help increase profits and marketability? An exception to this was the Harry Potter theme music (which has a good argument to be in the Top 5). Did the folks producing Harry Potter (knowing they already had a guaranteed jackpot) feel they needed music more to suit the movie and not to suit the suits (producers and marketing folk)?