The Abolition of Man ($9.99 US), the Collected Letters of C.S. Lewis, is free for Australian customers in the Kindle store. I don't expect it to be free for those in the US.
Book Description
In this graceful work, C. S. Lewis reflects on society and nature and the challenges of how best to educate our children. He eloquently argues that we need as a society to underpin reading and writing with lessons on morality and in the process both educate and re-educate ourselves. In the words of Walter Hooper, "If someone were to come to me and say that, with the exception of the Bible, everyone on earth was going to be required to read one and the same book, and then ask what it should be, I would with no hesitation say The Abolition of Man. It is the most perfectly reasoned defense of Natural Law (Morality) I have ever seen, or believe to exist. If any book is able to save us from future excesses of folly and evil, it is this book." This beautiful paperback edition is sure to attract new readers to this classic book.