A common
attack on
atheism is that without
God there can be no
morals.
This argument assumes that morality can only come from God - that human beings are unable to determine any type of moral code. It also seems to assume that people only know something is wrong because God decided it to be so.
It is entirely possible for a person to come up with a moral code without needing to look toward religion to dictate what it should be. One good starting point is respect for others - assuming that all people have the same rights, and not assuming yourself as the most important person there is. Once you've accepted this, then it is possible to determine what you should and should not do to others based on equality.
Morals without a religious source are also able to change when society changes, discarding useless ones and adding new useful ones.