Q: But if you don't believe in God, who do you think made you?
A: Sometimes, when a man and a woman are very much in love, they ... no, wait, wrong lecture.
Seriously, most atheists would answer this question with "My parents." And that would be it. They do not believe that an almighty Creator was involved in any way, just regular old people doing that regular old thing. A god is as unnecessary to explain human conception as it is to explain the conception of weasels.
But just because an atheist is someone who lacks God-belief doesn't mean that all atheists believe in metaphysical naturalism (the idea that the physical, natural world is all there is). For instance, a Buddhist atheist might believe that there is a non-material component to all life, which we are unable to measure through our normal senses, but which accrues various amounts of karmic debt. This insubstantial essence lives on beyond us, and in fact incorporates itself into future iterations of the self. In that sense, such a person might reply "My parents, me, and the karmic nature of the universe."
Most atheists, however, would likely consider this sort of non-divine supernaturalism as claptrap and nonsense. By far the most common answer is that we are created by the same mindless forces of nature responsible for every other living non-human creature we have ever seen.