Google Books lists nearly three million free e-books, which can be browsed by clicking on its Free Classics shelf and can be read on most devices, except for Kindles that aren't the KindleFire.
You'll need a library card, of course -- so if you don't already have one (more than 40% of Americans don't), borrowing free e-books might be a good reason to finally visit your public library and get a library card.
Sony continues to offer its popular and critically-acclaimed public library lending feature by offering patrons with a valid library card the ability to easily and conveniently borrow free e-books wirelessly from over 15, 000 public libraries in the US via an intuitive, simple-to-use dedicated icon on the device.