Over at Matthew Flannagan's website, Flannagan provides some great interaction with a writer from The Secular Outpost, Jason Thibodeau. Thibodeau raises a classic objection to Divine Command Theory, the "arbitrariness objection." Put simply, the objection is that if what is right is determined by God's commands, then God could command morally repulsive acts and we would be obligated to do what seems morally repulsive. Flanagan does an excellent job responding to Thibodeau's formulation of the objection. Also, there are a number of helpful links to some of Flannagan's other works if you're interested in digging a little deeper.