Project Gutenberg -- Over 30,000 books available for free. Has links to Gutenberg sites in other countries that also provide free online books
Global Text Project -- Free ebooks in six major subject categories.
HathiTrust Digital Library --HathiTrust is a partnership of major research institutions and libraries working to ensure that the cultural record is preserved and accessible long into the future. There are more than fifty partners in HathiTrust, and membership is open to institutions worldwide.
Digital Librarian: Electronic Texts, Primary Sources, Digital Libraries -- A large librarian-approved collection of links.
Humanities Text Initiative -- Links to full text resources in literature in English.
Internet Archive: Open Educational Resources -- Contains over 1,000 free university lectures, course materials, videos, and supplemental materials from universities in the U.S. and China.
The Literature Page -- Provides classic books, plays, stories, poems, essays, and speeches in the public domain online.
Textbook Revolution -- A student-run searchable collection of free electronic texts.
World Digital Library -- Digitized images of letters, maps, books, photographs, paintings, objects, and more from around the world, sponsored by the U.N. Education Agency.