Quite ninja'd before I finished, but I'll post it anyway.
I know it was mentioned like 10 pages ago, but I don't see how Buddhism would have anything to do with a really 'religion Vs. Athism' discussion. Buddhists don't beleive in a god or gods, they beleive in the teachings of one man who actuilly existed, it's more of a life philosphy than a 'religion' with a god or gods. Other religions should be fair game in this discussion though, like Hinduism.
Atheism is not necessarily limited to unbelief in God/gods, despite that being it's literal meaning. The reason atheism so often gets confined in such a way is that during the birth and growth of the idea, it has been a very much "western", or west-centrated, construct, pitted against the God of the Christian and Jewish mythologies. Modern atheism isn't just restricted to this or the "western" hemisphere, however, and so to expand it to other parts of the world, a broadening of the concept is required. Thus, atheism, especially modern atheism, should not be seen just as a standpoint on whether or not God exists, but on mythologies in general. Better defined as a point of view which questions the credibility of religion/myths/superstitions in general.
Besides, lots of Buddhist branches have gods, so atheism as unbelief in gods are still very much applicable to it.