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I like Pixel of Ink (http://www.pixelofink.com/category/free-kindle-books/). This list is only Amazon Kindle books. I subscribe to the daily email which lists both free books and some discounted books. Most of these books are fiction, often romance or action, and do seem to be short term freebies – but as long as you complete the “purchase” while the price is $0, you can build up quite a library and find authors that you enjoy.