Living Library
This site is collection of free ebooks that are entirely written and maintained by the general public. It is an interesting ideas and some the books I perused through were quite well developed. Two nice things about this site is that all of the books are under a GNU license and a lot of the complete works offer pdf downloads (which is great for printing and taking the document with you).
It have texts on everything from language learning, to cookbooks, to children’s books. It is a part of the Wikimedia Foundation (which is best known for its Wikipedia project).