Free ebook sources in many formats:
Inkmesh is a search engine that searches more than thirty online sources for free e-books. You can search by title or author.
Project Gutenberg, the original site for free text online, offers more than 33,000 free books that play nicely with any e-reader platform. You'll find mostly classics and public domain works here. No registration is required and the site is easy to use.
Baen Books, publisher of science fiction and fantasy, offers a number of their titles as free downloads. Established authors such as Eric Flint, Louis McMaster Bujold, Mercedes Lackey, and David Weber can be found here. You can save e-books to your computer or send them directly to a Kindle.
The Online Books Page from the University of Pennsylvania offers an index of hundreds of thousands of online books freely readable on the Internet.
Now that Kindle and Nook are open to file sharing, eBookFling offers users the chance to swap e-books for free with other readers nationwide while still retaining ownership. For every five books listed to loan out, users get one credit towards borrowing.
Interesting blogs for e-book readers:
The Digital Reader is a blog devoted to news, reviews, and opinions on eveything e-book.
Ebookanoid reviews e-readers, e-books, and the websites devoted to them.