I'm partial to the background Epcot music. It's part of the fountain music. I think to call it the Epcot Entrance medley, but I think it has another name in the real world. It gets stuck in my head every trip.
My other favorite is ofcourse PotC (So sad they took the music out of the first part of the ride).
There's also the orginal Tikibird song (They only play a fraction of it now, also very sad, cause the full lyrics are a hoot, if a bit dated. Who wears feather decorated hats anymore?)
Heffalumps and Woozles is cute.
I may also be the only person who misses the Mexico ride song. It was hard to follow some of the lyrics though.