History Notes/Outlines and Beyond- Click on the AP US History Tab. (VERY USEFUL)
http://histnotes.com/Homepage.html
Spark Notes- Click on the "Sparks Notes" tab and select History from the subject list
The National Archives Primary Sources
http://www.archives.gov/exhibit_hall/picturing_the_century/index.html
Two other good resources- Library of Congress and History Sage
CLEP: Study Resources
http://www.collegeboard.com/student/testing/clep/history_ss_resources.html#hss02