A variety of websites offer free e-books as part of a promotion, with publishers' permission, or because the book is out of copyright. Below are a few options you'll find online.
Amazon's top 100 free books for Kindle.
Barnes & Noble's featured free Nook books.
A collection of freely available e-books, audio recordings, and movies to download.
An open, editable library catalog, building towards a web page for every book ever published.
Many classic books that are in the public domain and freely available as e-books.