Library of Congress
http://www.loc.gov/index.html
They say it best: “The Library of Congress … [is] the largest library in the world, with millions of books, recordings, photographs, maps and manuscripts in its collections. The Library's mission is to make its resources available and useful to the Congress and the American people and to sustain and preserve a universal collection of knowledge and creativity for future generations. ”

Spending time exploring this site can be very rewarding. Check out the “American Memory Project,” for access to the library’s collections organized by topic. “Thomas” gives you access to legislative information and a wealth of political data and government resources. You can access global/international resources through the “Global Gateway.” This is only a small portion of the resources at your fingertips.