First of all.....

KelBelStar!

And as for sounds/music, there's several for me:

The BGM for at the beginning of Epcot and also for Innoventions Plaza/Fountain area.
Space Mountain Tunnel
The dog howl from HM.
The BGM for Adventureland and Tomorrowland.
The BGM for Sunset Boulevard and the area around MV3D.
Hearing the trailers before you reach the final "Theatre" room part of the queue for The Great Movie Ride.
The music played before Fantasmic!
The BGM from the beginning of AK, Chester & Hester's Dinorama area and Dinosaur.
And last but certainly not least, the first time you hear the music that's being played at the resort you are staying at.