A helpful follow-up to the book review from yesterday
From Theopedia: Penal substitutionary atonement refers to the doctrine that Christ died on the cross as a substitute for sinners. God imputed the guilt of our sins to Christ, and he, in our place, bore the punishment that we deserve. This was a full payment for sins, which satisfied both the wrath and the righteousness of God, so that He could forgive sinners without compromising His own holy standard.
Some additional resources:
http://voiceoftruthblog.com/a-survey-of-the-cross-the-atonement-part-1
http://voiceoftruthblog.com/substitionary-atonement-a-response
http://voiceoftruthblog.com/substitutionary-atonement-a-response-part-2
http://voiceoftruthblog.com/historical-baptist-view-of-substitutionary-atonement
http://voiceoftruthblog.com/the-devil%e2%80%99s-favorite-domino
http://voiceoftruthblog.com/the-suffering-servant
http://voiceoftruthblog.com/a-survey-of-the-cross-the-atonement-part-2