Their creator goes to great pains to lip synch to everything from rap to Mary Poppins to Animaniacs to Budweiser commercials.
Kingdom Hearts Random Crap: reams of silliness.
My favorite is Kingdom Hearts done as an Invader Zim episode, but for those who appreciate extreme potty humor, having Squall and friends singing the Mr. Hanky Christmas song from South Park probably deserves honorable mention.
Spoiler warning. Also volume warning: the main flaw of these things is some are loud, some are quiet, and one tends to have to reach for the volume control.