• American Labor Studies Center
• American Memory Project from the Library of Congress - thousands of documents, photos, maps, films, sound recordings, etc. from the collections of the Library of Congress, including women's suffrage, African-American pamphlets, George Washington's letter books, life histories from the WPA, American Revolution broadsides and much more.
• Avalon Project at the Yale Law School
• Beyond the Bubble - This website is part of the Library of Congress's Teaching with Primary Sources Educational Consortium.  The site uses primary resources to "go beyond the bubble" by offering easy-to-use assessments that capture students' knowledge in action - rather than simply testing their recall of discrete facts.  It is great for anyone who is teaching American history or working with NHD kids on U.S. topics.  Additionally, the assessments are aligned with the Common Core.
• Cornell Making of America Digital Library
• Documents for the Study of American History
• Duke University-Special Collections
• Electronic Text Center
• Electronic Texts
• Famous Trials
• Historical Text Archive
• Internet Archive of Texts and Documents: The United States
• JSTOR
• Making of America
• New Deal Network
• Online Speech Bank
• Primary Sources Research Colloquium
• Scholarly Resources Microfilm
• Turning Points In American History: The American Founding and Reconstruction - an NHD resource provided by ConSource

Civil War History

• American Civil War
• From Revolution to Reconstruction
• Secession Era Editorials Project
• U.S. Civil War Center

African American History

• Africans in America
• Documenting the American South
• Dred Scott Digital Archive
• Exploring Amistad Race and the Boundaries of Freedom in Antebellum Maritime America
• Freedmen and Southern Society Project
• Freedom's Journal
• Race and Place: African American Community Histories
• Roanoke Island Freedmens Colony
• Southern Oral History
• Tangled Roots

Native American History

• American Native Press Archives
• Kappler's Indian Affairs, Laws, and Treaties
• National Archives Records of the Bureau of Indian Affairs
• National Archives Records of the Indian Claims Commission
• Native American Documents Project
• Plains Indian Ledger Art Digital Publishing Project

Military History

• Air Force Historical Research Agency
• U.S. Army Center of Military History
• U.S. Army Military History Institute
• U.S. Navy History
• The Wars for Viet Nam

Colonial History

• Colonial Williamsburg History Explorer
• Plymouth Colony Archive Project
• Salem Witchcraft Trials
• Virtual Jamestown

US Government History

• Central Intelligence Agency - Electronic Document Release Center
• Core Documents of U.S. Democracy
• FBI - Freedom of Information Act - Reading Room
• Federal Land Patent Records
• FedStats
• Foreign Relations of the United States
• National Security Archive
• Oyez: Supreme Court Multimedia Database
• Resources for the Study of International Relations and Foreign Policy
• Supreme Court Opinions
• United States Historical Census Data Browser

Presidential History

• Abraham Lincoln Online
• Franklin D. Roosevelt Library and Digital Archives
• George Washington Papers
• Project Whistlestop
• THOMAS -- Legislative Information from the U.S. Congress on the Internet
• White House Historical Association

Immigration & Genealogy

• American Family Immigration History Center
• Genealogy Resources on the Internet
• Rootsweb
• USGenWeb Project

Women's History

• Elizabeth Cady Stanton and Susan B. Anthony Papers Project Online
• Women and Social Movements in the United States, 1830-1930
• Women's Studies: Women in the Jewish Community
• Worcester Women's History Project

Western US History

• America, Russia, and the Meeting of Frontiers
• New Perspectives on the West
• The Oregon Trail
• Web de Anza: An Interactive Study Environment on Spanish Exploration and Colonization of "Alta California" 1774-1776
• WestWeb: Western History Resource