Anything by Damian Conway: http://www.youtube.com/watch?v=ZAf9HK16F-A I've watched him give talks in Klingon. I've watched him explain how to build a supercomputer using laser printers. And who can forget that classic talk, "Temporally Quaquaversal Virtual Nanomachines"?
My favorite was his talk on SelfGOL, and I don't even like obfuscated code! (See http://libarynth.org/selfgol for an explanation of what SelfGOL is.)