Scot McKnight has made it to Galatians in his Pastor’s Bookshelf series on his Jesus Creed blog.
He mentions the commentaries of F. F. Bruce, Richard Longenecker, H. D. Betz, James D. G. Dunn and J. Louis Martyn in addition to his own in the NIV Application series. There is a wealth of commentaries on Galatians and I’m sure there are many that could be added to this list but keep in mind that it is intended for pastors. Should we be surprised that Ben Witherington’s Grace in Galatia is missing?
While not a commentary, I don’t think any pastor should preach on Galatians without referring to Interpreting Galatians: Explorations in Exegetical Method by Moisés Silva. (Baker, 2001) 080102305X, 9780801023057.