Primatologist and ethologist Frans de Waal presents the age-old question of morals without a God in the best way I can find.
His original article, "Morals without God?", presents the fascinating existing inclinations towards altruism (and what we'd call simple politeness) in the animal world, drawing justly cautious conclusions. The followup article, "The God-Science Shouting Match: A Response," written after 700 or so responses to the first, places the debate in the right context, asking the right questions.
Kudos to de Waal for dissuading the gut-level, pointless "pro-science/pro-god" dychotomy in favor of a far more reasoned, methodical view.