James Randi and Project Alpha

Project Alpha was a hoax orchestrated by the stage magician and skeptic James Randi. It involved planting two fake psychics, Steve Shaw and Michael Edwards, into a paranormal research project. The researchers became convinced that the pair's psychic powers were real. The hoax was later revealed publicly.

Wikipedia has a really interesting article on this project. Gotta love Randi and how he destroyed the pseudoscientific parapsychology field.