You can now get over 170,000 books on Amazon's Kindle, the e-Book reader that Amazon has had a hard time keeping in stock. 170,000. That's a lot of books! That # does not include all of the free content that you can pull down from the Internet onto your Kindle. It does not include the newspapers, magazines, and blogs also listed in the Kindle Store.
If you're looking for more free content, including books, take a look at ManyBooks.net for example, of FeedBooks.com. More such sites can be found in this nice collection put together by blogger Chris Koozie (Chris – hope I got your name right!)