Youtube has a couple BETA features that they are messing with right now
http://www.youtube.com/testtube
One of the things I tried on one of my videos is the audioswap where you take a song and it replaces your video's audio with the song. I tried it with the Nike Elevation Commercial.
http://www.youtube.com/watch?v=QBrBA-fCpBU
seems kinda cool, and def has some potential.
EDIT: Some of these hip-hop songs have really good beats.