American Founders Online: An Annotated Guide to Their Papers and Publications
http://www.loc.gov/rr/program/bib/founders/
"The digital resources described in this guide provide online access, in varying degrees, to the personal papers and/or publications of the major founders of the American Republic -- that is, those men who served in roles of national political leadership between 1765 and 1815 -- and members of their families." Included are John Adams, Samuel Adams, Benjamin Franklin, Alexander Hamilton, Thomas Jefferson, James Madison, George Washington, and others.

American Memory Timeline
http://memory.loc.gov/ammem/ndlpedu/features/timeline/index.html

America's Story from the Library of Congress
http://www.americaslibrary.gov/cgi-bin/page.cgi

Chronology of U.S. Historical Documents
http://www.law.ou.edu/hist/

Digital History of the United States
http://www.digitalhistory.uh.edu/

Explore America's Past Through Our National Parks
http://www.cr.nps.gov/colherit.htm#top

Making of America
http://quod.lib.umich.edu/m/moagrp/
Maintained by the University of Michigan, this is a digital library of primary source material on late 19th-early 20th century American history.

PBS-A History of US
http://www.pbs.org/wnet/historyofus/index.html

The American Presidency: a Glorious Burden
http://americanhistory.si.edu/presidency/home.html

The Charters of Freedom-The Declaration of Independence, the Constitution, the Bill of Rights
http://www.archives.gov/national_archives_experience/charters/charters.html

The Living Room Candidate: Presidential Campaign Commercials, 1952-2004
http://www.livingroomcandidate.org/

The Price of Freedom: Americans at War
http://americanhistory.si.edu/militaryhistory/