If you want the end all explanation of atheism just look at our friend Mariano's exhaustive essay on it called Atheism: a critical examination of its causes and effects .
Those unfamiliar with Mariano's work, visit his blog called Atheism is Dead.
The brilliant and well written essay's points really could be turned into hundreds of posts debunking atheists and still have a plethora of material left over. In fact some of the subjects, and quotes, have been talked about here in some past posts. Instead let it speak as a reasonable plea to help our atheist friends change their presuppositions and worldview.