Running the Books: The Adventures of an Accidental Prison Librarian (Steinberg). Since my wife used to work in a prison, this was a particularly insightful book.
The Faith Instinct: How Religion Evolved and Why it Endures (Wade). An intriguing premise - religion exists today because religious behavior conferred advantages to early humans.
The Master Plan of Evangelism (Coleman). An old classic that I've read before, I also like to call this book "The Master's Plan of Evangelism" since it is so much about what Jesus' strategies for reaching people would actually look like in our lives.