The center is located at the Harriet Beecher Stowe House and Library in Hartford, Connecticut, the city where Stowe lived from the 1860s to her death in 1896. Its website is a lovely and authoritative guide to Stowe's life and times.
Stephen Railton and his team at the University of Virginia have knocked it out of the park. This site is an incredible online library of primary documents related to Uncle Tom's Cabin.
Harriet Beecher Stowe wasn't the only distinguished member of her family. This site looks at the illustrious Beechers, a clan who made a heavy imprint on the American landscape. From Stowe's father Lyman Beecher, a noted clergyman, to her grandniece, the author Charlotte Perkins Gilman, the Beechers made important contributions to American faith, literature, and reform.
Uncle Tom's Cabin was inspired, in part, by Josiah Henson, a Maryland-born slave who escaped to Canada. He established the Dawn Settlement in Dresden, Ontario to assist former slaves. The settlement is now a historic site, and its website contains useful information about Henson and his cause.
Burns' mammoth documentary of the Civil War is an amazing educational resource. The companion website to the film is pretty great, too. It contains short, simple biographies of nearly every major player in the war, including Harriet Beecher Stowe.
The National Park Service runs this virtual tour of the Underground Railroad, the network of safe houses that allowed slaves to escape to the North. The site also points to locations that were not part of the Railroad but are significant to the history of slavery. These include Harriet Beecher Stowe's house in Cincinnati, where she held abolitionist meetings, and the house in Brunswick, Maine where she wrote Uncle Tom's Cabin.