This video has been one of my favorites for years, though it sounds like the writes have upgraded the music since I last saw it. Beautiful flash animation and the piece with the keyboard player is hilarious.
~Geo
Ps. Go to Albinoblacksheep.com or homestarrunner.com for some more good ones.
PPs. The Harry Potter Puppet Pals videos are funny too, especially with Ron being portrayed in such a falsetto.