Paul: Apostle of the Heart Set Free This is an outstanding orientation to Paul, the man and his ministry by the late University of Manchester scholar, F. F. Bruce.
Romans (Tyndale New Testament Commentaries (IVP Numbered)) This is an accessible and affordable introductory commentary to Romans by F. F. Bruce. It's an ideal entry-level text to Romans scholarship.
The Epistle to the Romans (The New International Commentary on the New Testament) This is one of the very best commentaries available. Prof. Moo combines outstanding scholarship with powerful spiritual insights.
Romans: The NIV Application Commentary: From Biblical Text to Contemporary Life Prof. Moo applies Romans to the practical issues of Christian living in the 21st century. This is an excellent resource for group Bible study.
Word Biblical Commentary: Volume 38A, Romans 1-8 The Word Biblical Commentary series is one of the finest available. This volume on Romans 1-8 by Prof. James D. G. Dunn is outstanding.
Word Biblical Commentary, Vol. 38B, Romans 9-16 Volume 2 of Prof. James D. G. Dunn's outstanding commentary covering chapters 9-16.
Romans This volume by Dr. J. A. Fitzmyer is one of the most worthwhile commentaries available on Romans. It is well worth the investment of your money and time.
Romans (N.T. Wright for Everyone Bible Study Guides) This short commentary on Romans by Bishop N. T. Wright is written with a scholar's mind and a pastor's heart.
The Message of Romans: God's Good News for the World (Bible Speaks Today) This is an excellent commentary for use in your Sunday school class or Bible study group. It is by leading Anglican evangelical scholar, Dr. John Stott.