The Gospel of John: A Commentary: Two Volumes. Hendrickson Publishers, 2003.
Keener is an expert Johannine scholar. This commentary is a beast! It opens up the world of John's (and Jesus') day in a spectacular fashion. This commentary should be number 1.
Revelation. NIVAC. Zondervan, 2000.
Keener is an expert when it comes to the 1st century Jewish, Greek, and Roman context. This is reflected in his commentary on Revelation. I really liked how he keeps to understanding the text from the context of John's day (even when dealing with future eschatological events). This made me give it 5 stars. The practical application parts are also very helpful for pastors and ministers. With such a valuable source, we don't need to shy away from preaching from the book of Revelation in our congregations.