The Online Books Page
Links to 35,000 free e-books.
Project Gutenberg
Links to ten’s of thousands of free e-books
Our World Book Encyclopedia subscription gives us access to over 5,000 e-books.
Google Books is another good and growing source, which will let you search the text of over 7,000,000 books and let you read samples of thousands. Many thousands are free and very easy to read. You can also look at and subscribe to many periodicals at Google Books.
Hongkiat.com is a graphics design blog that has a link to a number of free book sites. Some require a login or registration.
Another good site is Free e-Book Search.Net which has a lot of programming and technical books. A search there will link you a number of sites that might require a download or login and registration.