An Exposition of the Epistle of the Apostle Paul to the Galatians
Written in 1853 by John Brown, Professor of Exegetical Theology (Image, Text, PDF).

A Historical Commentary on St. Paul's Epistle to the Galatians
Published by Sir William Ramsay in 1899. Emphasis on historical context and archaeological insights. [partial e-text; work in progress]

Biblical Thinking: Galatians Commentary
Studies in Galatians by Pastor Darrel Cline containing detailed comments and personal application.

Commentary on the Epistle of St. Paul to the Galatians
By St. John Chrysostom. With preface by John Henry Newman and notes by Gross Alexander.