Update: Now that I've listened to the whole thing, I have to say Craig is in over his head and Kagan makes minced meat of him. I wish they had been more evenly matched.
Update II: Here's an interesting article by Wes Morriston (who linked to it in the Prosblogion comments) rebutting Craig: God and the ontological foundations of morality. And then there are the Stanford entries on moral arguments for the existence of god, moral realism, and moral naturalism.
Apparently God is as bad at grounding morality as Science.