My first point is actually addressed more at Christians than atheists. Christians sometimes think that if you are not a Christian you cannot behave in a morally right manner. This is, of course, absurd. All we need to do is look at non-Christians around us to see this. Non-Christians of every stripe are involved in charitable activities. Christians can work side by side with atheists in order to bring relief to the starving, or to stem the tide of AIDS in Africa.
Beyond modern anecdotes, we can look to the Bible and see examples of morally appropriate behavior from those who would be considered outside of God's covenant community. A good example is the Philistine King Abimelech in Genesis 26:7-11. Isaac, like his father Abraham, told the King that his wife Rebekah is actually his sister. Abimelech, however, sees Isaac caressing Rebekah in seclusion and realizes the truth. Isaac had feared that he would be killed because of his wife's beauty, but instead Abimelech makes certain that none of his subjects will harm them. Though Abimelech did not worship Yahweh, he still behaved in a morally commendable fashion on this occasion.
At this point an objector may attempt to make the point that a non-Christian, or more specifically an atheist, who behaves morally actually counts as evidence against the truthfulness of Christianity. On this understanding examples of morally upright atheists should undermine belief. Sam Harris expresses this sentiment in his Letter to a Christian Nation. "If you are right that religious faith offers the only basis for morality, then atheists should be less moral than believers. In fact, they should be utterly immoral. Are they?" This, however, represents a misunderstanding of what the Bible says about human beings. Harris is unfamiliar with the doctrine of common grace.
Christians have recognized from the beginning that those outside the faith can behave morally. In Romans 2:14-5 Paul writes, "For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them (ESV)." From the New Testament on Christian theologians have recognized the implications of this passage. It should not surprise Christians when secular physicians devote themselves to assisting the helpless in war-torn countries (one of Harris's examples). They are simply acting in accordance with the law God wrote upon their hearts. While it is possible that other religions may be vulnerable to this attack, Christianity is quite safe.