Probably the most famous collectible stamp ever minted,
this 1918 bit of postage is worth at least $600,000 dollars
if you happen to have one. Known as the "Inverted Jenny,"
the plane was mistakenly printed upside down. Only a single
sheet of 100 made it into circulation. Later this year the Post
Office will issue a souvenir sheet of six for actual use. But it
will be a $2 stamp. Shoot.