Spotting rare coins is a lucrative hobby for some, but it takes patience and impeccable eyesight. There are millions of dollars floating around in this market, many of which may be undiscovered.

The most valuable Roosevelt dime of all is the 1975 No-S proof, and that's because of a very rare minting mistake. In fact, it's one of the rarest US coins that exists, and there are only two known ...