The Library of Congress is the world's largest library and the largest body of knowledge under a single roof. Two new iPhone applications The Library of Congress Virtual tour (free), and The Library of Congress Reader(.99) give a fascinating look into the institution.
The Virtual Tour walks you through the Main Reading Room, The Great Hall and much much more. The Reader grabs the top stories from the Library and feeds them to your iPhone or Touch. All great stuff if you are into not just books, but a major part of American life, culture and history.