2½ Dollars (Panama–Pacific Exposition)

The Panama-Pacific Quarter Eagle: a sea-horse, a world's fair, and a coin almost nobody bought

In 1915 San Francisco threw the party of the century to show the world it had risen from earthquake and fire. The Mint struck a tiny gold coin for the occasion — and then melted almost a third of them when buyers stayed away. The survivors are now among the most prized commemoratives in American gold.