I remember the scores of a couple of movies I saw around ten years ago fondly:
1) the score to The Player, by Robert Altman, released in 1992. The music was by Thomas Newman, who's done a number of other movie scores, but I don't think any big hits (eg, he did "Green Mile" and "Shawshank Redemption", according to the Amazon links). I liked the music so much that I almost bought the soundtrack on CD then, but I didn't own a CD player at the time. Now, I just looked it up on Amazon, and they have one used copy, for $90!
2) The Thin Blue Line, a documentary by Errol Morris, had a great instrumental soundtrack by Philip Glass, who is famous enough that it's still in print.
As far as sound tracks that have popular music, I saw the movie version of Starsky and Hutch a few months ago, and it had a great cheesy '70's soundtrack.
Jess519 mentioned the movie Singles. I never saw it, but I've lived for 18 years two blocks south of the apartment building where Matt Dillon's character lived.
One night, I was waiting for the bus across the street from the building. It was about 40 degrees F., and raining, but they were filming that night, a scene that required Dillon to play a guitar while shirtless in the courtyard.
There was a guy standing at the bus stop to tell people waiting at the bus stop to be quiet during filming. But suddenly, a small dog with a shrill bark began to make a ruckus in the alley right next to the courtyard. The guy ran across the street to shut it up, but I've wondered whether the dog's voice was edited out, or left in to make it seem like a more realistic street scene.