The 1804 silver dollar. "The King of U.S. Coins" resoundingly reaffirmed its claim to that throne on Aug. 30, 1999, when the Childs specimen, the finest-known example of this famous American rarity, changed hands at auction for $4.14 million -- more than double the previous record for any U.S. coin at that time.
Known as "The King of U.S. Coins," the 1804 dollar is extremely rare, with only 15 known examples. No U.S. dollars dated 1804 actually were struck in that year; Class I specimens were struck in 1834-5 as diplomatic gifts (8 known), while Class II (unique) and III specimens (6 known) were struck during the 1850s for collectors. For more: http://worldsfairofmoney.com/museum-showcase/the-idlerbebee-class-iii-specimen-1804-dollar.aspx#