Book: The Problem of Pain by C. S. Lewis
Description: Why must humanity suffer? In this elegant and thoughtful work, C. S. Lewis questions the pain and suffering that occur everyday and how this contrasts with the notion of a God that is both omnipotent and good. An answer to this critical theological problem is found within these pages. (from Amazon.com)
I know this book isn't one of Lewis's better known books, but I felt God telling me to pick it up one day when I was feeling down. The timing was pretty perfect, too; about two weeks after I began reading The Problem of Pain, three of my acquaintances were in a train accident and two of them ultimately died. I found this book helpful as I was working through my questions and grief.
I actually ended up reading it twice, to give myself more of a chance to think about and reflect on what Lewis said. This was a very small book, not much over 100 pages, but there was a lot in there and a lot to think about. I found it very comforting, helpful, and insightful, even if I didn't agree with everything Lewis said (mostly about animal pain, which is admittedly something that's not discussed in the Bible very much). Lewis is so good at explaining thing with good, real-life examples.
I would highly recommend this book, especially to anyone struggling with this question.