The following are sources that I highly recommend (watch for frequent additions):
Kelly, G.B. and N. Burton, eds. A Testament to Freedom: The Essential Writings of Dietrich Bonhoeffer. San Francisco: HarperSanFrancisco, 1980.
Webber, Robert E. Ancient-Future Faith: Rethinking Evangelicalism for a Postmodern World. Grand Rapids, Mich.: Baker Books, 1999.
Webber, Robert E. Who Gets to Narrate the World: Contending for the Christian Story in an Age of Rivals. Downers Grove, Ill.: InterVarsity Press, 2008.
Wells, David F. Above All Earthly Powers: Christ in a Postmodern World. Grand Rapids, Mich.: William B. Eerdmans Publishing Company, 2005.
Wells, David F. God in the Wasteland: The Reality of Truth in a World of Fading Dreams. Grand Rapids, Mich.: William B. Eerdmans Publishing Company, 1994.
Wells, David F. Losing Our Virtue: Why the Church Must Recover Its Moral Vision. Grand Rapids, Mich.: William B. Eerdmans Publishing Company, 1998.
Wells, David F. No Place for Truth: Or Whatever Happened to Evangelical Theology?. Grand Rapids, Mich.: William B. Eerdmans Publishing Company, 1993.