Here's a great video by Vi Hart that shows a couple of proofs of the Pythagorean Theorem. Nothing new in terms of the proofs; they're ones I've seen often. What's clever about Vi's approach is that she uses paper-folding to create the elements of the proof. I like this kinesthetic approach to a couple of familiar proofs.
As always with Vi's exuberant videos, it would be nice to be able to watch them at half speed!