Guides
Pick up a copy of one of the most popular coin collectors' books, such as "Whitman's Red Book" and "The Official Black Book Price Guide." These books provide listings of the most valuable coins with pictures to help you identify them.
Time Frame
Some of the early coins minted in the 1790s and first part of the 19th century can be worth thousands of dollars in any condition due to their scarcity. Most American coins minted prior to 1965 comprised 90 percent silver, making them valuable for the metal content. The U.S. Mint continued to strike gold coins worth a dollar and more until the late 20th century. These coins are extremely valuable, but also quite rare.
Error Coins
Most modern coins only carry some extra value due to rare errors contained on them, and it is still possible to find some of them in change. A 1960 penny with the date double stamped, for example, can be worth hundreds of dollars if found in great condition.