Verse-by-Verse Commentaries:

Waylon Bailey, Micah, Nahum, Habakkuk, Zephaniah (New American Commentary), Broadman and Holman, 1998.
Adele Berlin, Zephaniah: A New Translation with Introduction and Commentary (Anchor) Doubleday, 1994. ****
Ehud Ben Zvi, A Historical-Critical Study of the Book of Zephaniah (Beihefte zur ZAW, 198), Walter de Gruyter, 1991.
John T. Carson, "Zephaniah" in The New Bible Commentary, Eerdmans, 1967: 773-780.
J. Alec Motyer, "Zephaniah" in The Minor Prophets, Vol. III, (ed. T. McComiskey), Baker, 1998.
Marvin A. Sweeney, The Twelve Propets, Vol. II, (Berit Olam), Liturgical, 2000.

Monographs, Compilations, and Studies:

Ivan Jay Ball Jr., A Rhetorical Study of Zephaniah, Bibal Press, 1988. ****
Paul R. House, Zephaniah: A Prophetic Drama (Bible and Literature, 16), Almond Press, 1988.
Arvid S. Kaperlud, The Message of the Prophet Zephaniah, [Oslo] Universitetsforlaget, 1975.
Daniel Hojoon Ryou, Zephaniah's Oracle Against the Nations: A Synchronic and Diachronic Study of Zephaniah 2:1-3:8
____ (Biblical Interpretation, 13), E. J. Brill , 1995.
Jonathan Stark (taped lecture series) ****1/2

Articles and Essays:

Adele Berlin, "Zephaniah's Oracle Against the Nations and an Israelite Cultural Myth" in Fortunate the Eyes that See: Essays in Honor of David
____Noel Freedman in Celebration of his Seventieth Birthday (ed. A. B. Beck, A. H. Bartelt, P. R. Raabe, and C. A. Franke), Eerdmans, 1995:
Ivan J. Ball, "The Rhetorical Shape of Zephaniah." in Perspectives on Language and Text:
Essays and Powems in Honor of F. I. Anderson's
____60th Birthday (ed. E. Conrad and E. Newing), Eisenbrauns, 1987: 155-67.
Michael DeRoche, "Zephaniah 1:2-3:  The 'Sweeping' of Creation," Vetus Testamentum 30 (1980): 104-109.
Philip J. Nel, "Structural and Conceptual Strategy in Zephaniah, chapter 1." Journal of Northwest Semitic Languages 15 (1989): 155-167.
Richard Patterson, "A Literary Look at Nahum, Habakkuk, and Zephaniah," GTJ 11 (1990): 17-27.

More Commentaries:

Elizabeth Achtemeier, Nahum-Malachi (Interpretation), Westminster John Knox, 1986.
Robert A. Bennett, "Zephaniah" in The New Interpreter's Bible, vol. VII, Abingdon, 1996.
David W. Baker, Nahum, Habakkuk, Zephaniah (Tyndale), Inter-Varsity, 1988.
Walter Kaiser, Micah, Nahum, Habakkuk, Zephaniah, Haggai, Zechariah, Malachi (Mastering the Old Testament), Word Books, 1992.
J. J. Roberts, Nahum, Habakkuk, and Zephaniah (OTL), Westminster/ John Knox, 1991.
O. Palmer Robertson, The Books of Micah, Nahum, and Zephaniah (NICOT), Eerdmans, 1994.
Ralph L Smith, Micah-Malachi, (Word Biblical Commentary, 32), Word Books, 1984.
Larry Walker, "Zephaniah" in Expositor's Bible Commentary, Vol. VII, Zondervan, 1985.

More Monographs:

More Articles:

Henk van Grol, "Classical Hebrew Metrics and Zephaniah 2-3" in The Structural Analysis of Biblical and Canaanite Poetry (JSOT Supplement, 74)
____ ed. W. van der Meer and J. C. de Moor, Sheffield Acedemic, 1988): 186-206.