Perhaps the most famous rare US Stamp, the Inverted Jenny, with its small print run and fanciful error, has been a golden goose for philatelists for over a century. Unlike other stamps on this list, there are 100 Inverted Jennys in circulation, but the wider availability makes the stamps even more sought after. The Inverted Jenny is a misprint of a 1918 stamp featuring one of the Jenny biplanes first used by the US Post Office to carry mail. The plane on the face of the stamp was accidentally printed upside down. The US Post Office released several million sheets of Inverted Jenny stamps in 2014 for the 95th anniversary of the misprint. Among the intentionally inverted stamps were 100 non-inverted sheets of stamps, a teasing tribute to the original mistake. The sheets of ‘Upright Jennys’ are collectors items in their own rights, selling for as much as $50,000. However, this publicity stunt did cause some controversy, as the US Post Office is not allowed to intentionally print errors.