CoinStudy has current numismatic values for all U.S. coins. Professional Coin Grading Services has its own price list that includes U.S. commemorative coins. In addition, the Numismatic Guaranty Corporation has a searchable catalog for foreign coins with price figures available for all mintings from 1600 to the present day.
A coin's potential sale price depends heavily on its condition, even in the case of extremely rare coins. However, regardless of date or condition, all silver and gold coins have a minimum value based on their precious metal content. All U.S. dimes, quarters and half-dollars minted before 1964 have a silver content of 90 percent, while half-dollars minted between 1965 and 1970 contain 40 percent silver.