After reading a couple of Oliver O'Donovan's works, my current to-read list includes:
Man and the State
by Jacques Maritain
Torture and Eucharist: Theology, Politics, and the Body of Christ
by William T. Cavanaugh
Theopolitical Imagination
by William Cavanaugh
The Blackwell Companion to Political Theology
edited by William Cavanaugh
Theology and the Political: The New Debate
edited by Creston Davis and John Milbank
After Christendom? How the Church Is to Behave If Freedom, Justice, and a Christian Nation Are Bad Ideas
by Stanley Hauerwas