In 1726, a woman fooled many people into believing that she had given birth to rabbits. In 1998, Burger King took out a full-page ad in USA Today introducing its new burger specifically designed for left-handed eaters. Alas, the ad was just an April Fool's Day joke.
These are but two of the incidents chronicled by the online Museum of Hoaxes, which allows you to browse hoaxes by type or year. It also includes links to sites that are, themselves, hoaxes, such as National Blonde Day and MalePregnancy.com.