One theistic argument is the moral argument (or axiological argument). It's the idea that in order to say that there are actual moral rights and wrongs, we have to presuppose a sort of metaphysical anchor or ground for these values that transcends individual cultures and epochs, something in fact which looks very much like the Judeo-Christian God. If we reject such a ground, then we are left with pure relativism, where nothing is actually right or wrong. This may be OK when the issue under discussion is whether you should be completely forthcoming on your taxes, but when we point to horrific atrocities, it becomes very difficult to say that there is simply nothing morally wrong going on.
However, rather than defend this argument, I want to point to an interesting reaction to it. Many atheists who hear the moral argument misunderstand it to mean that atheists cannot be moral people or upstanding citizens. If you need to believe in God in order to believe that rape is wrong, then you're essentially arguing that if you don't believe in God, then you must not believe that rape is really wrong. But of course, this isn't the argument. The point, rather, is that the moral judgment "rape is wrong" -- made by theist and atheist alike -- must have a metaphysical ground in order to be valid. Thus, according to the moral argument, the atheist is being inconsistent in affirming that rape is wrong while denying that God exists. But this does not mean that atheists don't know right from wrong.
Now part of the reason I find this reaction interesting is that I could present a parallel argument which almost certainly would not provoke the same reaction. Say, for example, I argued that in order for mathematics to be possible we have to posit a metaphysical foundation for numbers, a Platonic realm of forms, which is best understood as the mind of God (such arguments have been made). So in order to affirm that 2 + 2 = 4, we have to presuppose something like the Judeo-Christian God. How many people would misunderstand such an argument to mean that if you don't believe in God, you don't really believe that 2 + 2 = 4? I suspect very few, if any. Yet this argument is exactly parallel to the moral argument: in order to affirm X we have to presuppose a metaphysical foundation for it that is best understood as God.
So why are some people so liable to misunderstand the moral argument? Again, I suspect (although I could very easily be wrong) it's because our views on morality are inextricably bound up with our views of ourselves: what we do and what we think should be done says a great deal of what kind of person we are. So when someone tells an atheist that her worldview is inconsistent with believing that rape is wrong, she reacts. Instead of realizing that the moral argument is saying something about the relationship between her worldview and moral beliefs, she only sees it as saying something about her moral beliefs, and thus about herself: whether she is a good person.
(cross-posted at Quodlibeta)