Kindle has been growing in popularity day by day and the release of New White Kindle eReader & Tablets(New Fire, Fire HD) that are cheap at price and better at features than the iPad is not going to change the trend any sooner.
Amazon officially releases free books for kindle from time to time. The offer may be short lived but once you download, the book stays free with you forever.
What are you waiting for ? Download free Kindle EBooks.