Running Scared by Ed Welch is free right now on Kindle. Other Kindle deals
Also Westminster Books is running a great initial sale as they introduce the ability to purchase ebooks that will be read on Kindle. You can get 2 books of your choice from Crossway books for the next 24 hours or so. You can see the list of books here. There are over 300 to choose from. I found the process of getting the ebooks relatively simple but if you need help they are willing to walk you through the process from what I understand.