Boston.com has a very cool chart detailing how to mess with your mind's perceptions, naturally. I think the most interesting one is definitely the first one. It tells you how to hallucinate with ping pong balls and a radio. If you'll excuse me, I need to go cut some ping pong balls in half and listen to static for the next hour or so.
Link
@ DylanDoom, I literally LOLed at visualizing that.