Super Mario Physics
Super Mario Physics was a surprising find for me. I've seen many Mario Flash tributes, and most of them turn out to be very un-funny. But Mario Physics does a lot of things right. There's good voice work, both with the narrator and using Mario sound clips appropriately. The animations are fantastic, this guy actually animated Mario himself, and it's well done, something which is usually lacking from Flash films.
But what was even more surprising was that the humour actually took a backseat to teaching physics. This is an educational Mario video, and although it is funny, this could easily be shown in a classroom setting and be a huge hit.
Be sure to check it out, especially when Mario breaks the sound barrier in the name of science.