For those in want of further eading, let me recommend the following:
Carson, D.A. ‘Atonement in Romans 3:21-26.’ In The Glory of the Atonement: Biblical, Theological, and Practical Perspectives, eds. Charles E. Hill and Frank A. James (Downers Grove, IL: IVP, 2004), 119-39.
Gathercole, Simon. ‘The Cross and Substitutionary Atonement.’ SBET 21 (2003): 152-63.
McGowan, A.T.B. ‘The Atonement as Penal Substitution.’ In Always Reforming: Explorations in Systematic Theology, ed. A.T.B. McGowan (Leicester, England: IVP, 2006), 183-210.
McKnight, Scot. A Community Called Atonement (Nashville: Abingdon, forthcoming 2007).