Digital National Security Archive (DNSA)This database maintains full-text access to "more than 63,000 of the most important declassified documents regarding critical U.S. policy decisions" during the 20th century.
A excellent resource for those looking for primary sources relating to, among many other events, The Berlin Crisis (1958-1962), Cuban Missile Crisis (1962), Iran-Contra Affair (1987), and Nicaraguan / U.S. relations (1978-1990). Unlike the DDRS, above, this database concentrates exclusively on documents relating to U.S. foreign policy after World War II. Another minor difference between the two databases involves the manner of release and provenance of the documents available. Many documents in DDRS were originally requested by researchers through NARA's network of presidential libraries, whereas many DNSA documents came to light as the result of executive branch compliance with the 1966 Freedom of Information Act (FOIA).