As of 2015, many websites, including CoinStudy.com, PCGS.com and CoinSite.com list values of American gold coins. These sites provide updates on varying schedules, so the listed prices serve as guidelines rather than absolute current values.
CoinStudy.com's listings for gold coins include considerable detail, noting the features of each coin and giving a chart comparing the value of coins in differing conditions. These details allow the user to assess the value of a particular coin more accurately, rather than just having a ballpark figure for that type of coin. Having a formal assessment by a reputable coin dealer done remains the only way to be certain of the exact current value of a particular coin, however.