Unlike Internet Archive, Project Gutenberg finds books from all publication dates and lets you download them for free at almost any format for any device (iPad, Kindle, Sony Reader, iPhone, Android). There books are 100% legal and free because they let you download books that are out of copyright in the United States. With their partners they have over 100,000 books. Great site, it even has banned books if that interests you and more. So before you purchase a rare/unique book online check this site if it has it. Click on the link below to get to Project Gutenberg.