Books on the Internet
Project Gutenberg has a collection of over 45,000 eBooks available free to the public. You can read them online, download ePub files, and Kindle books.
OpenLibrary.org has over 20 million records with a goal to create a web page for every book. Similar to Wikipedia, the public can edit and contribute entries and records. The eBooks can be checked out, read online, or downloaded in multiple formats.
The Internet Archive provides access to 6,000,000 public domain eBooks that can be read online and downloaded.
More than 29,000 eBooks are available free through ManyBooks.net. The eBooks can be read using most eReader devices.
Over 285,000 books/printed materials are available online through the Library of Congress website.
Google Books provides a preview and sometimes the entire text of a book for the public to browse. If the book is in the public domain, you can download the item in PDF form.
The Audio Archive has a collection of thousands of audio recordings such as audio books, live concerts, poetry, podcasts, and old radio programs. Many of the files are free to download.
Volunteers of LibriVox.org record audio files of books in the public domain. These are free and open to the public for listening and downloading.
Academic and Research Resources
The University of CA Press has 700 eBooks available to the public which can be read online or printed.
Created by the National Academy of Sciences to publish reports and books related to scientific, technical, and health related issues, the National Academies Press offers over 4,000 books and titles that can be downloaded in PDF form.
HathiTrust.org offers public access to millions of titles from international academic and research institutions. Most articles archived by the Hathi Trust and their partners can be read online.
More Online Resources
The University of Pennsylvania Library has an extensive list of many other free online texts and indexes. They range from very specialized to general and also have many resources for foreign language texts.