Today is the feast day of St. Thomas Aquinas, so it would be a great day to give at least 2.975 cheers for Natural Law theory, and to thank God that the Muslims weren't the only folks in the 13th century reading Aristotle.
As a model for intelligent, faithful, winsome engagement of a pagan world, Aquinas is hard to beat. In many ways, we face a similar world: one that uses cultural and intellectual tools foreign to ours to make sense of reality. In his day, Aquinas made use of those tools, including "pagan" philosophy, and co-opted them in the light of revealed truth, to engage the ideas, people, and institutions around him.
May we do the same!
Suggested readings, then, on this topic:
Thomas Aquinas, Treatise on Law (Regnery Gateway 1996)
GK Chesterton, Saint Thomas Aquinas: The Dumb Ox (Doubleday 1956) (1933)
Curtis Chang, Engaging Unbelief: A Captivating Strategy from Augustine & Aquinas (InterVarsity 2000)
James K.A. Smith, Who's Afraid of Postmodernism? Taking Derrida, Lyotard, and Foucault to Church (Baker 2006)
Stephen J. Grabill, Rediscovering the Natural Law in Reformed Theological Ethics (Eerdman's 2006)
J. Budziszewski, Written on the Heart: The Case for Natural Law (InterVarsity 1997)