Crazy Love - by Francis Chan.
I heard Pastor Chan speak at Catalyst about two years ago and was really impressed. I don't think he was the best speaker at the conference, but he certainly stood out. He was so passionate about helping others in their relationship with Christ that it just poured out of him. It was almost as if he couldn't stand up straight because of the pain of the moment. He was that into it. That same passion comes out in his book, Crazy Love: Overwhelmed by a Relentless God.
We recently finished an adult study on the book, and I have seen some positive fruit from it. Each chapter is a challenge and I encourage anyone who reads it to do so with a partner or in a group. A lot of times we are challenged and we simply read it and move on. But if you study this in a group setting, it forces you to wrestle with the issues and to deal with them. You cannot hide. While I don't agree with every single line of the book, (I don't think we ever will), I would still recommend it. Make sure you get it and study it with your group.