For those in the US on mobile, or lazy.
http://www.amazon.com/The-John-Calvin-Collection-Classic-ebook/dp/B00AVYSUQQ/
http://www.amazon.com/The-Martin-Luther-Collection-Classic-ebook/dp/B00AVYXEE4/
http://www.amazon.com/Collected-Works-John-Bunyan-PergamonMedia-ebook/dp/B00VKFL1KC/