I came across this site yesterday: ManyBooks.net - Ad-free eBooks for your iPad, Kindle, or eBook reader. There are thousands of older — out-of-copyright — titles here. I have downloaded a couple — each is available in many formats including those indicated in the link above. Exploring the site I discover, for instance, 48 titles by G.K. Chesterton. The variety is so great that it is almost necessary to know beforehand what you are looking for.