This is an attempt to gather as many of the sources for free ebooks that are available online into one place. If you know of any other websites that legally host free ebooks or if any of my links are broken, please comment to let me know. Note that I am only interested in legal sources; I'm not particularly interested in getting sued for copyright infringement.
The Ohio EBook Project - http://ohdbks.lib.overdrive.com (Note: requires Overdrive Media Console software)
Netlibrary - http://www.cincinnatilibrary.org/resources/netlibrary.asp (Note: requires a Cincinnati library card number and pin to sign in)
Google Books - http://books.google.com/
Project Gutenberg - http://www.gutenberg.org
Sony Reader eBooks - http://ebookstore.sony.com/category/free-ebooks (Note: requires the Sony Library software)
Barnes and Noble Free Nook Books - http://www.barnesandnoble.com/u/Free-eBooks/379001668/ (Note: requires registration)