Atheists by definition believe that God does not exist (here's an example). Because of this, they look at the world from a very different perspective than theists do. In particular, they see through an extremely different lens than Christians do.
I disagree with atheists on almost all issues, whether they be spiritual, moral, educational, political, etc. This makes sense since the atheist sees the world as ultimately meaningless. Followers of Jesus Christ should see the world as having great meaning because God Himself created it.
Atheists offer little that is of value to this world. If they hold to a consistent worldview, then they must believe that their lives have absolutely no significance.
However, atheists are good for one thing: they stand for the existence of absolute truth.
Atheists not only believe that God does not exist, but they also believe that this is absolutely true. It is objectively true. It is true for everyone. It is, as evangelical apologist Francis Schaeffer famously said, "true truth."
Atheists strongly believe this. They argue for it. They have reasons (faulty, of course) for why they believe what they believe. They want everyone to believe what they believe. Atheists believe that if everyone would just reject the existence of God, then the world would be a better place.
While Christians should obviously disagree with atheists' conclusions, we can agree with them that absolute, objective truth exists. We can agree with atheists that God either exists or He does not. We can agree with atheists that God cannot be true or real for some people but not for others.
We can stand with atheists against today's scourge of postmodern thought. Postmodernism is a worldview that says that objective reality does not exist. What one person sees may be valid and real for him, while it may be completely different for others. No one can know anything for certain about all things.
Postmodernism stands against Christianity, but is more insidious than atheism. The reason for this is that a postmodernist will not argue with a Christian about the existence of God. He will simply say something like this, "It's fine for you if you believe in God. That's true for you. However, what is true for me is that... (fill in the blank)."
Postmodernists stand firmly against the existence of absolute truth. In fact, the only absolute they adhere to is that absolutes do not exist. Yes, there is irony there.
If there is no objective truth, then there is no room for discussion of anything that matters. If there is no objective truth, then there is no Christianity.
However, Jesus said that He is the truth (not the truth for only some people).
Therefore, we as Christians should agree strongly with atheists that absolute, objective truth exists. We must stand against postmodernism at all costs. This is what atheists are good for.
We must then sit down with the atheist next door and politely discuss the scientific facts - all of which point to biblical creation.