Kind of related, not really, but interesting video over at Reason TV
http://reason.tv/video/show/622.html
I wasn't inferring Mao Tse Dong and Stalin committed genocide for "atheistic" reasons and, to be fair, I think LgrrrR was being sarcastic when he asked that. But, I was offering these two, and there are more -- generally communists and fascists that have probably killed more people than all the religious wars combined...including Muslim-incited wars.
Seriously, it's hard to top the approximately 120 million people that died at the hands of Mao, Stalin, and Hitler.