Cool proof that I've never known. It's not part of my middle school math curriculum this year, but the story is very relatable to kids. A great number of middle school aged kids could draw great confidence out of themselves in seeing how they can also share in some of Einstein's wonder of the world.
I've often fell back on the area of squares proof, but for so many, it never "clicks" with them. The general concept of area, I've found, repeatedly befuddles so many kids.
Einstein's proof uses fractions of the areas of two similar triangles formerly part of the original right triangle. In keeping with triangles and some simple inverse operations, I think I might have found a nice new tool for relating the Pythagorean theorem to my students.