AMDOCS: Documents for the Study of American History: Houses digital documents from the years 800-2005.
American Journeys: A digital collection of early American exploration and settlement.
American Presidency Project: Comprehensive site by the University of California, Santa Barbara that includes a variety of presidential papers, addresses, speeches, etc.
Army Heritage Center: Includes primary sources related to American soldiers.
Avalon Project: Documents in Law, History and Diplomacy: A website with centuries-worth of legal documents collected and presented by the Yale Law School Lillian Goldman Law Library.
Bill of Rights Institute: Includes a great page on primary source documents of the Founding Fathers.
Black Past: An expansive collection on African American history.
Digital History: Site includes online exhibits, primary source documents, and topic ideas on American history.
Documenting the American South: Produced by the University of North Carolina at Chapel Hill, the website offers a variety of sources regarding the history and culture of the American South.
Famous Trials: Site hosted by the University of Missouri-Kansas City (UMKC) School of Law reviews trials spanning from 399 B.C. to 2006 A.D.
Foreign Relations of the United States: An incredible collection from the University of Wisconsin of various documents related to America's policies with other nations around the world starting in 1861.
HarpWeek: Website devoted to the history and articles published in Harper's Weekly. Features unique political cartoons, particularly those from Thomas Nast.
History: Africa: Hosted by the University of Washington Libraries, the site has several helpful links to primary and secondary sources concerning topics specific to Africa.
History: Asia: Hosted by the University of Washington Libraries, the site has several helpful links to primary and secondary sources concerning topics specific to Asia.
History: Latin America: Hosted by the University of Washington Libraries, the site has several helpful links to primary and secondary sources concerning topics specific to Latin America.
History Matters: Website of the American Social History Project Center for Media and the Center for History and New Media that includes surveys of American history and numerous primary source documents.
History of the United Kingdom: Primary Documents: A collection of Brigham Young University with links spanning hundreds of years of British history.
Mark Twain Project: Houses the collections of Mark Twain's letters and writings.
National Archives: Home to many of America's national treasures, many of which have been digitized for online use. The Declaration of Independence, Constitution, and Bill of Rights are available on their Charters of Freedom page. The site also hosts online exhibits. Be sure to also check out Founders Online and Digital Vaults.
National Museum of Australia: Primary Sources: Online collection of a variety of topics related to the history of Australia.
Open Collections: Sponsored by Harvard University, the site has an expansive system of digital collections that include items over a 400 year span of history. Collections include: the Islamic Heritage Project, Expeditions and Discoveries, Contagion: Historical Views of Disease and Epidemics, Immigration to the United States, 1789-1930, Women Working, 1800-1930
Oral History Online, Bancroft Library, UC Berkeley : Collection of transcribed interviews conducted by the Regional Oral History Office ranging in a variety of topics and time periods.
POTUS: Presidents of the United States: Provides overviews, speeches, and writings of the U.S. Presidents as collected by the Internet Public Library.
Smithsonian Institution: The world's largest museum and research complex at the click of a mouse. The Smithsonian Institute also boasts several online exhibits and digital collections.
Supreme Court Database: Home to over two hundred pieces of information about Supreme Court decisions between 1946-2012.
World War I Document Archive: A collection of Brigham Young University with links to treaties, diaries, images, biographies and more.