Lee's Illustrated Stamp Listopedia 1999 

U.S. Inverts

When part of the design of a stamp appears upside down because of a printing mistake, it is called an invert.   Inverts are often very rare and valuable to collectors.  These are the nine varieties of United States inverts that have reached the public.
Landing of Columbus invert Landing of Columbus The 15-cent issue in a series of two-color stamps depicting American symbols and history.  Three stamps in the series produced errors.  (1869)
Declaration of Independence invert Declaration of Independence The 24-cent issue, after a painting by John Trumbull. (1869)
Shield, Eagle and Flags invert Shield, Eagle and Flags The 30-cent is the rarest of the 1869 inverts. (1869)
Fast Lake Navigation invert Fast Lake Navigation The first of three stamps in the Pan-American Exposition series which encountered printing errors that resulted in inverted centers. (1901)
Fast Express invert Fast Express Only 158 copies of the 2-cent Pan-American Expo error are known to exist. (1901)
Automobile invert Automobile The vignette of an electric automobile is inverted in the 4-cent. (1901)
Dag Hammarskjold invert Dag Hammarskjold After a small number were discovered with the yellow background inverted, the Post Office intentionally reprinted the error, so that it is now worth little more than the rightside-up variety. (1962)
CIA invert Candle and Rushlight Holder Nicknamed the "CIA invert" because 95 of the 100 existing inverts were sold to members of the CIA. (1979)
Curtiss Jenny invert Curtiss Jenny The most famous of U.S. stamps is the airmail "inverted Jenny." (1918)


See also
Link Which Way is Up? Smithsonian National Postal Museum's stories of  inverts.
Link The Object at Hand Smithsonian Magazine article on the Jenny invert.
Link Poor Jenny! Report of how a $100,000 Jenny invert was vacuumed up by the cleaning woman.
Marzulla, Elena (ed.).  Pictorial Treasury of U.S. Stamps, Omaha: Collectors Institute, 1974.