http://www.wowio.com
Sponsored by Verizon, this site allows 5 free ebook downloads per day, once you become a member (also free).
I have downloaded several books on Ancient Egypt/Rome/Greece that are required or suggested for our curriculum (Winter Promise QAW). They have textbooks, activity books, fiction, poetry, encylopedias, etc...all are actual "books" in pdf format (so far anyway) and like the library, a few books may have questionable content, but you do not have to download any book you do not want.
These are not public domain books, they are mostly books that are current (well, from what I have downloaded only one was published more than 5 years ago). The site is updated almost daily with new materials.