Project Gutenberg is a volunteer-driven collaborative project that offers free online books. Books are primarily older works that have fallen out of copyright in the United States. Many titles may be downloaded to eReaders via ePub or Kindle format. The site also includes some audio recordings.
Google Books includes many full text, copyright free books in addition to copyrighted, non-full text materials. Search the site for a word, author, title, and then select "Free Google eBooks" along the left side to see the full text books.
Open Library is a partnership of libraries to offer Interlibrary Loan of eBooks directly to library patrons. Account holders can borrow eBooks from the site. St. Mary's University is a participant in the Open Library initiative. Create an account to start using Open Library. Take a look at the How It Works page for more information.