Bibliomania has been on the net for a couple of decades, and is now on the web. It's the backbone site to all book sites. Given to the internet community as part of the love people have for books..
 

Celebrating 10 years listing free books on the Web, this Library site has a ton of books.

Alex Catalogue of Electronic Texts  this started as a project out of Berkley and has since grown into it's own company, sortta like Yahoo and Netscape did.


World Wide School Library  This site has books for kids,


Great Books Online  This site contains many classical collections like the Harvard Classics, the King James Bible, Gray's Anatomy and other great reference books.  Definitely bookmark this one on your laptop for when you are traveling and need reference books.  Has books of quotations also for when you need help in writing a speech.