Rare Stamps

Rare stamps can be found in nearly all of the postage systems in the world, and are often over a century old. Two of the best known rare American stamps are the "Inverted Jenny" (which is actually a printing error) and the "1-cent Z grill" stamp.
Just two 1-cent Z grill stamps exist, and only one is available to stamp collectors. The other is in the collection of the New York Public Library. Both of them are now on public exhibition at the Smithsonian's National Postal Museum in Washington, D.C. (through October 1, 2007).
Other rare and famous stamps include the Treskilling Yellow, Penny Black, Blue Penny, British Guiana 1c magenta, and many others.