what are the most rare coins?
['The Top 15 Most Valuable Half Dollars.', 'The Top 15 Most Valuable Dimes.', "The 1913 Liberty Nickel - The World's Most Hyped Coin.", 'The 1933 Saint-Gaudens Gold Double Eagle.', 'The Flowing Hair Silver Dollar (1794)', 'Profile of the 1895 Proof Morgan Silver Dollar.', 'The Top 15 Most Valuable Pennies.']