This debate at Friendly Atheist has been interesting, but it seems to be going nowhere fast. The primary areas of contention is whether there are non-atheist methods for determining right and wrong, what these might look like, and whether they provide viable alternatives to theistic morality.
Some background reading:
Atheism and Morality (South Sea Republic)
An Atheist Responds (Christopher Hitchens in the Washington Post)
Atheism, Morality and Religion (Infidels.org)
Godless Moral Values (Austin Cline)
Michael Gerson: Asking Questions about Atheists–Answering them for Atheists (Rank Atheism)
Atheism and Morals Part 1: The evolution of morality