The Online Books Page
If you are looking for something to read or just want to browse through a vast selection of public domain literature, check out The Online Books Page at The University of Pennsylvania. There are over 30,000 titles in this collection, and it is searchable by author, title and subject. If you are looking for any book that has been around so long that the copyright has expired, this is the place to start.
The Online Books Page lists websites where books are published as HTML, has links to different Project Gutenberg text files, and links to page image files at different libraries around the world. There is a lot of effort being put into digitizing old books by the different libraries around the world. If you are looking for literature that has been out of print for a while or just like reading old books, check out this page.