"Be Mature: Growing Up In Christ" by Warren Wiersbe
This book is extremely well written and I'm really enjoying digging into it. It is a commentary, with a few questions at the end of each section. And believe me, Wiersbe knows his stuff! If you really want to dissect the book of James, pick this one up.
"James" by Max Lucado
We are currently studying James in the small group that we hold at our house, and this is the book we're using for our 12-week study. It's mostly discussion questions...with a little commentary along the way.