Common, scarce and rare U.S. Double Eagles ($20 Gold Pieces; Liberty Head; Saint-Gaudens) at Mintmark.com; also links to other issues of Eagles and U.S. gold bullion coins (American Eagle; American Buffalo; First Spouse).
"The largest denomination of all regular United States issues was authorized to be coined by the Act of March 3, 1849. Its weight was 516 grains, .900 fine [gold]. The 1849 double eagle is a unique pattern and reposes in the Smithsonian. The 1861 reverse design by Anthony C. Paquet was withdrawn soon after being struck. Very few pieces are known . . . [also see, Gold Eagles] . . ." — 2010 "Red Book"