Calisphere

http://www.calisphere.universityofcalifornia.edu/

Calisphere is the University of California's free public gateway to a world of primary sources. More than 150,000 digitized items — including photographs, documents, newspaper pages, political cartoons, works of art, diaries, transcribed oral histories, advertising, and other unique cultural artifacts — reveal the diverse history and culture of California and its role in national and world history. Calisphere's content has been selected from the libraries and museums of the UC campuses, and from a variety of cultural heritage organizations.

American Memory

http://www.loc.gov/ammem/
The Library of Congress has digitized over a dozen of their primary document collections about U. S. history. This website also includes high-quality lesson plans.