Library of Congress - Digital Collections: American History
National Archives - America's Founding Documents
National Archives - Research the Archive's records
History Channel - Explore topics
U.S. History - an online textbook
Digital History - media, documents, and an online textbook for U.S. History
The American Yawp - An online American History textbook
MI Open Book Project - Eighth-grade US History textbook
Boundless U.S. History - another online textbook
American Historama - U.S. History for kids
Crash Course: US History (videos)