10ofthose.com has a good deal on The Prodigal God by Tim Keller
"In The Prodigal God, New York pastor Timothy Keller uses the story of the Prodigal Son to shine a light on the central, beautiful message of Jesus: The gospel of grace, hope and salvation. Keller argues that the parable of the prodigal son, while Jesus' best-known parable, is also his least understood. He introduces the reader to all the characters in this timeless story, showing that it concerns not just a wayward son, but also a judgemental older brother and, most importantly, a loving father. This short but powerful book is a reminder to the faithful, an explanation to the seeker and finally an invitation to all - both older and younger brothers - to enter in to the 'unique, radical nature of the gospel': the reckless, spendthrift love of God."