Postage Stamps
The most commonly known form of stamp, postage stamps are printed by the U.S. Postal Service for use in paying for mail delivery. Postage stamps come in a range of values, from 1 cent to $17.50 (as of 2011). U.S. postage stamps have no monetary value, however, and are good only for mailing letters or packages. Postage stamps never expire. If the face value of the stamp is less then the amount required to mail a letter, the sender needs to attach enough additional stamps to cover the difference.
Food Stamps
The first food stamp program was in May 1939, when unemployed factory worker Mabel McFiggin began collecting stamps to buy excess butter, eggs and prunes in Rochester, New York. The stamps were issued by the U.S. government to help needy people during the Great Depression, and to unload surplus wheat and other commodities bought by the government to support farm prices. The program faded after the Second World War, but was successfully revived in 1959. In 1964 Congress passed the Food Stamp Act, making the program a permanent part of America's social welfare system.
Collectible
Derived from the Greek words philos, meaning love, and atelia, meaning an exemption from tax, philately is the study of stamps and postal history, and philatelist is the term for people who collect stamps. Collectible stamps are either too rare or too valuable to be used for mailing letters. The rarest and most expensive stamp is the 1855 Sweden Three Skilling Banco, Yellow Color Error. Mistakenly printed on yellow paper instead of the usual green, this one-of-a-kind stamp sold at auction for $2.3 million in 1996.
Commemorative
The U.S. government issues commemorative stamps to honor or remember significant dates or memorable moments in U.S. history. Released in limited numbers, commemorative stamps are larger than everyday stamps and are more sought-after by collectors. The first commemorative stamp issued by the Postal Service was the "New World" stamp in 1983, which commemorated Columbus' discovery of the Americas.