Here's a classic April Fools Day prank:
In 1996 the Taco Bell Corporation announced that it had bought the Liberty Bell from the federal government and was renaming it the Taco Liberty Bell. Hundreds of outraged citizens called up the National Historic Park in Philadelphia where the bell is housed to express their anger. Their nerves were only calmed when Taco Bell revealed that it was all a practical joke a few hours later. The best line inspired by the affair came when White House press secretary Mike McCurry was asked about the sale, and he responded that the Lincoln Memorial had also been sold, though to a different corporation, and would now be known as the Ford Lincoln Mercury Memorial.
Happy April Fool's Day, everyone!