The App Store at iTunes has a new Library of Congress Tour for iPhone, iPad, and iPod Touch. A nice app that makes you want to hop on a plane and see the real thing. From the iTunes description:
The Library of Congress is the world’s largest library and the largest body of knowledge under a single roof. Whether you’re onsite, at home, in a classroom or elsewhere, this app will give you a virtual tour that mirrors the Library of Congress Experience, an award-winning group of exhibitions and features that has drawn record numbers of visitors.