I appreciated reading the NIV Application Commentary for Galatians myself. I used it and Longenecker’s commentary (mentioned above) to help prepare for a Sunday School class on Galatians that spanned several months. I recommend both books. Both were excellent and both left a mark. That study deeply affected my thinking.
I believe it was Scot’s commentary that limned two circles: Spirit and flesh. Spirit = fruit of the Spirit stuff, Flesh = everything else (including my best efforts). That was like throwing a stick of dynamite under an arctic ice sheet. The rumble was small at first, but then the effects kept rippling through, changing the landscape of my thinking.
I hope I have not misrepresented or misused your work, Scot! Paul’s original letter continues to be a powerful statement on its own. But I certainly recommend Scot’s and Longenecker’s commentaries to go along with it.

I misspelled my own name in #1!
Not a scholarly commentary per se, but I think Constable’s notes can be a worthwhile reference. He often has a number of good footnotes. Even if you disagree with his conclusion on a given topic I think his discussion is often worth reading.
He has notes for each book of the Bible. Here is the link for Galatians:
http://www.soniclight.com/constable/notes/pdf/galatians.pdf

Scot,
I recommend your commentary to many! Personally, I find Richard Hays very theologically rich commentary in the New Interpreter’s Bible to be most useful. He combines New Perspective elements, Salvation-historical (with focus on Paul’s use of Scripture) and apocalyptic.

I preached through Galatians a couple of years ago, and while there are some great commentaries out there (yours included, Scot), I found a series of lectures by Gordon Fee to be both helpful and delightful–a great listen! They’re entitled “Galatians in a Week,” from Regent College (similar to Wright’s well-known “Romans in a Week” lectures). Fee has a new commentary on Galatians, but I’ve not been able to use it. But I highly recommend the lectures.

I would definitely add to the mix: Ben Witherington’s Grace in Galatia. As well as the aforementioned Fee and Hays on Galatians. They’re very helpful for preaching/teaching on this intense epistle.

Coming Soon: Brian Vickers in the NCC edited by Michael Bird and Craig Keener.

Don Garlington has an excellent FREE commentary you can download from the Paul Page:
http://www.thepaulpage.com/Shorter_Galatians.pdf

Certainly these two by Richard Hays: The Faith of Christ (not a commentary, per se) and his section on Galatians in the New Interpreter’s Bible series.

Gordon Fee’s “Pentecostal Commentary”,
Hays in the NIB (which picks up on Martyn’s apocalyptic themes but seems more balanced),
Dunn’s book on the theological issues in Galatians,
Wright’s “entry-level” commentary,
and some of the papers that Wright has on the web.
Now, I also read some of the typical “old perspective” commentaries and it was as if they were talking about another book!

To all those mentioned, I would add Walter Hansen’s work from IVP. I have found it to be quite good – richly condensed – despite a place or two where I disagree with him. A lay person should have little trouble with him.