"The Last Olympian" and "Freebird"
Rick Riordan's Percy Jackson series is fantastic, btw. I just finished the final book, "The Last Olympian". No spoilers -- just a weird experience. In the last quarter of the book, I read this line:
Besides, we know this drakon they cannot beat.
"We know this drakon they cannot beat" -- there was something familiar about the cadence of that sentence. I was sure it was some song lyric, with "drakon" fitting in the place of some other word or words. I kept rereading it, and tada! my brain suddenly decided that it was from Lynyrd Skynyrd's Freebird (popup warning).
Except it isn't. There's really no similarity between "We know this drakon they cannot beat" and "And this bird you cannot change". But there it was, stuck in my head. I could go no further down that path.
But honestly, if you need a song in the back of your head as a soundtrack to the battle of Olympus, "Freebird" rocks.