University of Virginia Library - Electronic Text Center - contains thousands of publicly accessible books in electronic format. 

Project Gutenburg - web site of the first and the largest Public Domain digital library with over 5000 titles in ascii text format (e-text readable by just about any computer).  This project was started in 1971 during the early days of computing and the founder held that ". . . the greatest value created by computers would not be computing, but would be the storage, retrieval, and searching of what was stored in our libraries."  The Project Gutenberg Philosophy is to make information, books and other materials available to the general public in forms a vast majority of the computers, programs and people can easily read, use, quote, and search. 
 
University of Virginia Library - the electronic presence of the library at the University that Thomas Jefferson helped create. 

The On-Line Books Page is a website that facilitates access to books that are freely readable over the Internet. 

National Archives & Records Administration  "is an independent Federal agency that helps preserve our nation's history by overseeing the management of all Federal records. Here you can find the cornerstone documents of our Government -- the Declaration of Independence, the Constitution of the United States, and the Bill of Rights." 

Library of Congress  "If ever a library had a single founder, Thomas Jefferson is the founder of the Library of Congress. His personal library is the Library's core, and the vast range of his interest determined the universal and diverse nature of the Library's collections and activities. The active mind was central to Jefferson's concept of government; he felt there was 'no subject to which a Member of Congress may not have occasion to refer.' He believed that self- government depended on the free, unhampered pursuit of truth by an informed and involved citizenry. Today's Library of Congress epitomizes Jefferson's faith in learning and his practical determination to make democracy work." -- taken from the Preface of The History of the Library of Congress. 
 
America's Library - designed primarily for young people, this extension of the Lirbray of Congress, has many fun stories and little known facts about America.  This site wants you to have fun with history while learning at the same time. They want to put the story back in history and show you some things that you've never heard or seen before.  Even adults will find it interesting. 
 
The Internet Public Library - The Internet Public Library (IPL), is a public service organization and learning / teaching environment at the University of Michigan School of Information. 
 
Luminarium - provides a starting point for students and enthusiasts of English Literature. Nothing replaces a quality library, but hopefully this site will help fill the needs of those who have not access to one. Contains text and other supplemental material of Medieval, Renaissance and 17th Century English Literature. 

Bartleby: Great Books Online - "The preeminent Internet publisher of literature, reference and verse providing students, researchers and intellectually curious with unlimited access to books and information on the web, free of charge." 

Stanford Encyclopedia of Philosophy - a dynamic reference work in which each entry is maintained and kept up to date by an expert or group of experts in the field. 

Digital Library List - Google web directory of digital libraries.