Excellent thread idea! :glow:
Well, aside from the more general references you've all mentioned, I really love when music because part of the plot, or an actual character. Two movies that come to mind (I believe the latter was in homage to the former):
The Graduate - which was the first film to incorporate an entire soundtrack by a single music artist/group with music made just for the film.
Risky Business
In both these films there's a single moment when you hear the music, it's pounding away, the hero/protagonist (Dustin Hoffman and Tom Cruise, respectively) are in the process of driving a car - when the car stalls and the music stops with it.
Two of the most comedic uses of music ever, and very, VERY funny. The first is when Dustin Hoffman's character is driving to rescue Elaine from her wedding, and he's cruising south down Highwawy 101, rushing along in his little roadster, when his car starts to sputter and stall. The music - the instrumental part of Simon and Garfunkle's "Mrs. Robinson" - sputters and stalls, too. Freakin' hilarious (turns out he's out of gas).
In Risky Business, Tom Cruise's partents are away and have left him in charege of the house with explicit instructions not to do certain things - including driving his father's Porsche. But his friends (naturally) egg him on, so he gets in and the music pounds and he starts to back out of the garage and the music continues to pound and you know he's going to go drive off like a maniac in his father's souped up sports car - and the car suddenly stalls, the music stalling with it. He hasn't even made it out of the driveway! :lol:
In both cases the music is used to emphasize the sense of anticlimax, and becomes a visceral part of the plot, not just background or emphasis for the storyline.