You might find this site useful:
http://www.liberliber.it/biblioteca/index.htm
It has over 1500 e-books in Italian, most of them are the full text of public domain books and the few copyrighted texts are distributed with permission of the author.
Most of the e-books are available in three formats : txt, pdf and rtf.
The site is completely in Italian, you can browse its catalog by author, title or topic.