I am an atheist and a moral realist (apparently unlike Vodalus).
I don't see any reason to suppose why you need God to be moral. What's right and wrong is ultimately about the well-being of others. You should want other people to treat you as you would want to be treated. If you treat people indifferently then you can't justify yourself if you want them to be nice to you.
Euthryphro's Dilemma questions the assumption that God is the source of morals. It is asked thus:
Is what is good so because God commands it, or does God command it because it is good?
If the former, then morality is arbitrary because God could have said anything was moral and it would have been so. He could have said rape and murder was moral and that would make it so. If the latter, then morality exists outside of God.
Some apologists try to dodge the bullet by claiming that God is good, and therefore he cannot command something that isn't good. However, how would you know God is good? The only way would rest on trusting God to tell the truth, but if he's an evil God then you would expect him to lie about it, just as much as you'd expect a good God to tell the truth.
And then, if the only reason you are moral is to get into heaven and avoid hell, then it would seem like the morals of Christmas movies could defeat you. It is only about the presents? Shouldn't it be more than that? Shouln't you be good for the sake of goodness, regardless of whether you're being offered a reward?