While Edward Jones makes it clear that he went to no great lengths to research his novel, The Known World, the book did provoke our interest in learning more about the reality of slavery. Here are a few resources I've been exploring:
The Library of Congress offers excerpts from Born in Slavery: Slave Narratives from the Federal Writers' Project, 1936-1938 These narratives were collected in the 1930s as part of the Federal Writer's Proejct of the Works Progress Administration. Some audio is also available, or try the documentary, Unchained Memories, made from these interviews.
The PBS series Africans in America has a website offering a resource bank of documentation, illustrations and interviews.
The University of Virgina also offers an image bank --"The Atlantic Slave Trade and Slave Life in the Americas: A Visual Record."
Finally, for another unusual slant on the topic, the New York Historical Society offers an online exhibition on Slavery in New York.