Verse-by-Verse Commentaries:

Joseph Fitzmyer, Philemon (Anchor), Doubleday, 2000.
E. Earle Ellis, "Philemon" in The Wycliffe Bible Commentary, The Southwestern Company, 1968: 1397-1399.

Monographs, Compilations, and Studies:

Norman Peterson, Rediscovering Paul: Philemon and the Sociology of Paul's Narrative World, Fortress, 1985. ****
Charles G. Dennison
(sermon series, 1998) ****1/2

Articles and Essays:

James T. Dennison, "Paul, Philemon, Onesimus, and the New Creation in Jesus Christ," Kerux.
Danny Olinger, "A Redemptive-Historical Consideration of Philemon," Kerux.
Lee Irons, et al., "Theodoret of Cyrhus: The Epistle of Paul to Philemon," WTJ 61.1 (1999): 111-17.

Other Commentaries:

Markus Barth and Helmut Blanke, The Letter to Philemon (Eerdmans Critical Commentary), Eerdmans, 2000.
Cain Hope Felder, "The Letter to Philemon" in The New Interpreter's Bible, vol. XI, Abingdon, 2000: 881-905.
Joseph A. Fitzmyer, "The Letter to Philemon" in The New Jerome Study Bible, Prentice Hall, 1990: 869-870.

More Articles:

David M. Russell, "The Strategy of a First-Century Appeals Letter: A Discourse Reading of Paul's Epistle to Philemon,"
____ Journal of Translation and Textlinguistics 11 (1998): 1-25.
David L. Allen, "The Discourse Structure of Philemon: A Study in Textlinguistics" in Scribes and Scripture (ed. D. A. Black): 77-96.
A. H. Snyman, A Semantic Discourse Analysis of the Letter to Philemon" in Text and Interpretation: New Approaches in the Criticism
____ of the New Testament (New Testament Tools and Studies, 15) ed. P. J. Hartin and J. H. Petzer, E. J. Brill, 1991: 83-99.