As technology gets cheaper and better, the fanmade stuff that appears on the 'net' gets astronomically cooler. Whittling it all down to a top five (in order) is pretty hard, but there are some that just stand out from the rest, especially the Harry Potter vs. Star Wars video, which is completely unreal.
5. The Future of First-Person Shooters
4. Jedi Kittens Strike Back
3. Superman With a GoPro
2. Old School vs. New School
1. Harry Potter vs. Star Wars aka Wizard vs. Jedi Knight