The Inverted Jenny

The inverted Jenny (or Jenny Invert) is a United States postage stamp of 1918 in which the image of the Curtiss JN-4 airplane in the center of the design was accidentally printed upside-down; it is probably the most famous error in American philately. Only 100 of the inverts were ever found, making this error one of the most prized in all philately;

A block of four inverted Jennys was also sold at a Robert A. Siegel auction in October 2005 for US$2.7m. And in November 2007 an inverted Jenny was sold for US$977,500. In December of 2007, a mint, never hinged example, meaning one not previously affixed to a stamp album, was sold to an unidentified Wall Street executive for $825,000.

British Guiana 1 Cent Black on Magenta

British Guiana One Cent Black on Magenta, 1856 was considered to be the world's rarest and most expensive stamp. The stamps were printed on poor quality paper in black ink on magenta coloured paper. There’s only one in the world known exist, so this stamp was unique, as no other copy was ever discovered. In 1980 it was auctioned to John Dupont for $935,000.