My friend John Loftus has a short video on his site Debunking Christianity, about the Problem of Evil. While some of the video relates to moral evil (what man does to man or animals), much of it relates to natural evil (what God or nature does to man or animals). Christians typically use the argument that man's free will is responsible for all the evils we see in the world and God is not responsible. However, man's free will has nothing to do with the presence of natural evil.
I think this is a powerful video: