2 Corinthians: Finding Strength in Weakness (Life Guide Bible Studies)
The lifeguide series is a great series for group Bible study.
This study guide presents Paul's second (biblical) letter to the Corinthians in eleven group sessions. The questions are easy to understand and provide a lot of opportunity for discussion, not just simple one word or yes/no type questions. Each chapter usually had our group of 10-15 in discussion for about an hour.
I highly recommend this book and series to anyone wanting to start a Bible study group.