Wikipedia is keeping track of Web 2.0 pranks. And if you’re interested in the origin of April Fools, they’ve got that covered too.
Favorite prank:
Taco Liberty Bell: In 1996, Taco Bell took out a full-page advertisement in The New York Times announcing that they had purchased the Liberty Bell to “reduce the country’s debt” and renamed it the “Taco Liberty Bell.” When asked about the sale, White House press secretary Mike McCurry replied with tongue in cheek that the Lincoln Memorial had also been sold and would henceforth be known as the Ford Lincoln Mercury Memorial.