I love that website Scott!
Oh, and Scott, don't forget to mention that has more than just books; they have videos, audioclips/books, saved/archived webpages, and software, too!
Two other cool open resource sites include
Project Gutenberg and
OverDrive.
Project Gutenberg adds and archives as many books as possible that enter the public domain. OverDrive lets you borrow eBooks and audiobooks from your public libraries without having to travel to them. If you can't borrow it then, you can place a hold on the book.
Throwing in just a little tidbit, the
School of Open has free courses
online about "openness" in the world and why it is important along with how to find and make the most of creative commons resources.