$4,451,000 The Benjamin Franklin Z Grill, also known as the Z-Grill, is a 1-cent postage stamp issued by the United States Postal Service in February 1868. Featuring Benjamin Franklin’s profile, this stamp stands out with its unique “Z” grill pattern, which creates tiny indentations in the paper. Only two Benjamin Franklin Z-Grill stamps exist—one belongs to the New York Public Library, and the other is in private hands. In 1998, the 1868 1-cent Z-Grill sold for $935,000 to Mystic Stamp Company. Later, in 2005, it was traded to financier Bill Gross for a block of four Inverted Jenny stamps worth nearly $3 million. (Getty Images)