The U.S. Postal Service is nearly out of business, but rare stamps are still a booming trade. A 1856 one-cent stamp from British Guiana sold for $9.5 million at Sotheby's on Tuesday, breaking the record for the most valuable object by weight and size and the most expensive stamp ever sold at auction. The stamp is the only of its kind to exist and was owned by multimillionaire John E. du Pont, who killed a champion wrestler in 1996 and died in prison four years ago. According to du Pont's will, most of the proceeds will go to former Bulgarian wrestler Valentin Jordanov Dimitrov.