I find myself recommending G.K. Chesterton's "St. Francis of Assisi" to people from time to time, and with the new pope taking the name Pope Francis, it is perhaps more timely than ever for us to re-study the life of the original St. Francis. I can think of no more delightful introduction than G.K. Chesterton's biography. It's a slim, easy read and available in various editions. If you want to save money, you can read it free on the internet. Here's one source: http://archive.org/stream/francisofassisi00chesuoft#page/n9/mode/2up
* Previous posts on Chesterton:
G.K. Chesterton: Unfailing in Wit, Wisdom, and Sanity