I made a list of the scores and soundtracks most likely to get stuck in your head. These are the movies where all you have to do is hear the title of the movie and you start humming a tune. Whether you like it or not, which is the most memorable?
Run Lola Run
Unleashed (Massive Attack)
Broken Flowers
August Rush
Apocalypse Now
Easy Rider
The Graduate
Last Tango in Paris
Garden State
Once
Exotica
Besides the most obvious ones you mean? Star Trek, Star Wars, X Files, Batman, Superman......
I would say, if this was a game show, Id have to say Footloose.
I remember getting out of the moviehouse after seeing this and running across the street to the shopping center music store and grabbing the soundtrack. They ran out in 5 minutes.
One that took a while to jump out at me is Pleasantville. There is one scene in particular with two seminal bebop tunes: "So What," by Miles Davis which flows right into "Take Five" by the Dave Brubeck Quartet. I thought that was a brilliant use of music. Also, At Last by Ella Fitzgerald is also brilliantly placed.
The most memorable soundtrack EVER is difficult to ascertain. If you mean a noticeable song then I think the following are debatable as being the best:
The most current movie but cannot be considered "ever" is STAR WARS: the main theme, Darth Vader march, etc.
Then there is:
JAWS: The shark theme is EVERYWHERE.
BRIDGE ON THE RIVER KWAI: The whistling march song is forever.
WIZARD OF OZ: The march song of the evil witch's palace.
THE GOOD, THE BAD, AND THE UGLY: That famous whistle (what is it with the whistle tunes?)
INDIANA JONES: Indy's theme is not a whistle, thank God.
JAMES BOND FILMS
THE PINK PANTHER