William Lane Craig recently handily defeated Sam Harris in a debate titled, "Does Good Come From God?" (link to debate) Mr. Harris provided a very limited attempt to ground an atheistic morality in his opening speech. After that, virtually all of his arguments were simply either anti-theistic or simply anti-Christian. Those arguments were pretty clearly off the topic. In fact, they were demonstrated to be off topic in Sam Harris' own response to the very first audience question.
Mr. Harris' defeat was partly due to his approach of being unable to present any grounding for atheistic morality. Partly Mr. Harris' defeat was ensured by Prof. Craig's avoidance of reliance on the premise "God exists."
Mr. Harris' defeat was also partly due to the fact that his attempt to ground morality involved a significant and obvious category error. Mr. Harris argued that the worst possible world would be one in which all sentient beings suffered a maximum amount for a maximum duration. He argued that this "worst case" provides an objective reference point from which morality can be judged. However, that is not a maximally immoral universe, just a maximally unpleasant (for sentient beings) universe.
Prof. Craig pointed out this problem and Mr. Harris' response was extremely weak. He tried to argue that Prof. Craig has to grant Mr. Harris' premise because hell (the realm of the immoral) involves suffering and consequently the aim of mankind is to seek the pleasure of heaven as opposed to the misery of hell. However, this simply confuses the reward/punishment in a particular system with the means by which it is accomplished.
Moreover, for the atheist, this life does not provide heaven/hell-like reward/punishment. Often a person who causes great suffering receives little suffering himself in this life. Moreover, there is no obvious correlation (in this life) between reducing overall suffering and obtaining reward.
Therefore, as Prof. Craig pointed out repeatedly, while an atheist may have morals, he has no foundation for them. He cannot give a reasoned account of his morals. He may think that the Holocaust is dreadful, but he cannot give you an authoritative answer to the question, "Says who!" in response to his moral condemnation.
Mr. Harris didn't do himself any favors by essentially accusing Christians of being psychopaths (and then saying he wasn't doing that -- and then doing it again). However, Mr. Harris delivered his speech in a very calm and measured tone, and maintained his cool despite some fairly solid hits he was taking from Prof. Craig.