Digital History is a collaborative effort between the University of Houston, the Chicago Historical Society and other institutions to support the teaching of American history in at the elementary, high school and college levels. This beautiful and well-designed site includes an online textbook, encyclopedia, an interactive timeline, online exhibitions, and much more. The site also features a searchable database of over 1,500 annotated links to additional American history resources, audio archives (Real audio), and an image archive. Really fantastic stuff.