Uncle Tom's Cabin and American Culture site:
http://www.iath.virginia.edu/utc/
is a multi-media archive containing primary material including texts, images, songs, and film clips. It also has a search mode, interactive timeline and lesson plans for student projects.
The American History Online Site:
http://longman.awl.com/history/activities_14_2.htm
uses Uncle Tom's Cabin to explore the history of that era.
Uncle Tom's Cabin Resource Page:
http://www.humboldt1.com/~jedwards/uncle.html
includes links to biographical, historical, and criticism of Harriet Beecher Stowe and her groundbreaking novel.