From their website:
The Digital Public Library of America brings together the riches of America’s libraries, archives, and museums, and makes them freely available to the world. It strives to contain the full breadth of human expression, from the written word, to works of art and culture, to records of America’s heritage, to the efforts and data of science.
Sounds awesome! Surf on over there.
Also, there is an article in The Atlantic about the launch.