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Wikipedia has a few nice proofs of the pythagorean theorem. Elementary, but elegant.
Pythagorean Theorem, picture proof http://upload.wikimedia.org/wikipedia/commons/thumb/7/70/Pythagoras-2a.gif/220px-Pythagoras-2a.gif
Pythagorean Theorem, picture proof http://upload.wikimedia.org/wikipedia/en/5/56/Pythagorean_proof.pngPythagorean Theorem, picture proof http://upload.wikimedia.org/wikipedia/commons/thumb/7/70/Pythagoras-2a.gif/220px-Pythagoras-2a.gif
Pythagorean Theorem, picture proof http://upload.wikimedia.org/wikipedia/en/5/56/Pythagorean_proof.png