Dunn, James D. G.The Theology of Paul the Apostle. Eerdmans, 1997. Uses Paul's letter to the Romans as the foundation for a monumental study of Paul's theology.
Murphy-O'Connor, Jerome.Paul: A Critical Life. Clarendon, 1996. An exhaustive historical contextualization of Paul's life; shows Paul's indisputable importance in determining the shape and direction of Christianity.
Storr, Catherine.St. Peter and St. Paul. Raintree Steck-Vaughn, 1987. The role of the two saints in the early history of the Christian Church; for younger readers.
Wilson, A. N.Paul: The Mind of the Apostle. Norton, 1998. Especially valuable for situating all that is known about Paul's life within the greater context of the Roman Empire.