Among my all-time favorite April Fools Day hoaxes is the Great Swiss Spaghetti Hoax in which 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.
The announcement was accompanied by footage of Swiss peasants pulling strands of spaghetti down from trees. Huge numbers of viewers were taken in and 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."
More great hoaxes here.