The Aluminum Penny From 1974
When copper was worth a lot of money, the U.S. tried to produce stamped pennies made of aluminum. But the idea was later stopped and almost all of the 1.5 million created got melted down. Some, however, did not.
Only two have been found thus far. Their scarcity makes collectors believe that one of these coins would be valued at a quarter of a million dollars. Wow!