http://museumofhoaxes.com/hoax/aprilfool/#1: The Swiss Spaghetti Harvest
1957: The respected BBC news show Panorama announced that thanks to a very mild winter and the virtual elimination of the dreaded spaghetti weevil, Swiss farmers were enjoying a bumper spaghetti crop. It accompanied this announcement with footage of Swiss peasants pulling strands of spaghetti down from trees. Huge numbers of viewers were taken in. Many called the BBC wanting to know how they could grow their own spaghetti tree. To this the BBC diplomatically replied, "place a sprig of spaghetti in a tin of tomato sauce and hope for the best."
#2: Sidd Finch
#3: Instant Color TV
#4: The Taco Liberty Bell
#5: San Serriffe
1977: The British newspaper The Guardian published a special seven-page supplement devoted to San Serriffe, a small republic said to consist of several semi-colon-shaped islands located in the Indian Ocean. A series of articles affectionately described the geography and culture of this obscure nation. Its two main islands were named Upper Caisse and Lower Caisse. Its capital was Bodoni, and its leader was General Pica. The Guardian's phones rang all day as readers sought more information about the idyllic holiday spot. Only a few noticed that everything about the island was named after printer's terminology. The success of this hoax is widely credited with launching the enthusiasm for April Foolery that gripped the British tabloids in subsequent decades.
Related:
#6: Nixon for President
1992: National Public Radio's Talk of the Nation program announced that Richard Nixon, in a surprise move, was running for President again. His new campaign slogan was, "I didn't do anything wrong, and I won't do it again." Accompanying this announcement were audio clips of Nixon delivering his candidacy speech. Listeners responded viscerally to the announcement, flooding the show with calls expressing shock and outrage. Only during the second half of the show did the host John Hockenberry reveal that the announcement was a practical joke. Nixon's voice was impersonated by comedian Rich Little.