What is yours?
Mine is both highly recommended and very affordable. Also, if you get the Kindle version, instantly accessible!
John Barclay's Paul: A Very Brief History
Written by one of the world's leading Pauline scholars and author of the best "thick" book on Paul in recent years, this quickly read book is neatly divided in two parts, The History and The Legacy.
In a relatively few words the reader receives a summary of Paul's writings, a summary of Pauline scholarship, and numerous insights into that Paul's writings mean for the world today.
This award has nothing to do with a very nice lunch I had with John at the annual Aotearoa New Zealand Association for Biblical Studies in Dunedin recently :).
Seriously, it was a great privilege for all conferees to attend to a presentation John gave on Paul's theology of gift. We sat at the feet of a modern master!