From the Spaghetti tree to H.G. Well's Martian Invasion broadcast, the media playing tricks on the public is an April Fool's tradition.
The Museum of Hoaxes has compiled a list of the top 100 April Fool's Day hoaxes of all time. My personal favorites are#7: Alabama changing the value of pi and #51: SmelloVision.
For the other 98, click here.