Every month, Amazon.com has a list of 100 titles available in the kindle format on sale for $3.99 or less. Here are the ones that jumped out at me this morning (all aff links):
Brain Rules for Baby: How to Raise a Smart and Happy Child from Zero to Five by John Medina. I own his book Brain Rules and I've checked out Brain Rules for Baby from the library before. At this price, I don't mind buying it and having it always on hand for reference. Medina adheres to the theory of evolution, but the advice he dispenses is based on replicable scientific studies. (For example, if he says the human body is designed to run 12 miles every day, even though this is his evolutionary belief, he has studies that can be repeated to back it up.) One of the points he likes to make is that there are no credible studies to support the notion that those womb sound machines have any beneficial effects for the unborn baby, so this book isn't just what to do with your child, but what NOT to do or what NOT to waste your time or money on.
Churchill : The Unexpected Hero by Paul Addison. I'm not a Winston Churchill fanatic, but I want to know much more about him than I do currently. Some speculate that he was dyslexic and/or had ADHD. This book is 300+ pages, so it's not going to be a fluffy overly-brief and generalized biography.
Remember, you don't need to own an Amazon kindle in order to read kindle books. You can download a kindle app for your PC, laptop, Mac, BlackBerry, Android, iPhone or iPod Touch and so forth. Just click here: free Amazon kindle reading apps. You could also buy a kindle, and if you just want a kindle for reading books, I recommend the Paperwhite (with which I will most likely replace my current kindle Touch):
UPDATE: Actually, I will NOT be replacing my current kindle with the paperwhite because my kindle has text-to-speech, and the paperwhite lacks this feature. So if you want text-to-speech, you pretty much need to buy a Kindle Fire.