Oh, this could be a huge answer. I collect film scores and soundtracks; a lot of nifty music gets created or compiled for films. Maybe my all-time favorite film score is Spartacus (1961) by Alex North: thundering, epic, emotional and often sexy. Not in the same league, but a well thought-out use of pre-existing songs is Donnie Darko (2001), though that may be my growing-up-in-the-Eighties talking. I'm glad that when writer-director Richard Kelly did that odd re-cut version of the film, he was finally able to use the song he'd wanted for the opening, INXS's "Never Tear Us Apart," and move Echo and the Bunnyman's "The Killing Moon" to another spot in the film that was, he felt, more appropriate for it.
Day 09 - Best scene ever
I can't narrow it down. Maybe one of the scenes from the WKRP Thanksgiving episode, but you need the build-up of several scenes for that payoff. (Oh my God, that payoff.)
Or maaaaaaybe the last scene of the last episode of Newhart deserves that honor. I just saw clips from that again, and that still KILLS.