Mozart’s Eine Kleine Nachtmusik in various adaptations.
It isn’t just for ringtones.
Kids’ version:
Adapted for an Italian black-and-white film about Mozart’s life:
Jazz show choir version:
Metal version:
Tenacious D (Jack Black and Kyle Gass version [Warning! Offensive language] — starts at 1:03):
Professor O'Connell's Music History Blog: Class Assignments, Readings, Listening Examples, and Random Stuff 