I use Overdrive to borrow free books from my library frequently. It was easy to sign up with my library card number and once I find a book that I want to borrow, it is downloaded to my Kindle app. Amazon.com has great prices on ebooks and they frequently run deals so that you can find many that are very cheap or even free! My time is limited as a busy working mom of 3. I don't have time to browse through the thousands of books on the Amazon site each day to find ones that I may like so I let others do that for me. Here are my favorite sites that will notify you of new deals on Kindle books at Amazon:
Hundred Zeros - http://hundredzeros.com/
The Prudent Pantry - http://www.theprudentpantry.com/
Pixel of Ink - http://www.pixelofink.com/
Do you have a favorite place to find cheap or free ebooks? Let me know in the comments!