First of all we should define our terms.

Let's define 'faith' as a belief of something without evidence and 'religion' as an institution which is organized around the question of god.

In order to make any existential claim, including "there is no chair in front of me" down to "there is no god" one has to have a belief framework which inevitably has a set of first principles which are not proved with evidence. This is true of any belief - and therefore any belief, including the belief in the chair or the belief/disbelief in the existence of god, will require faith at some level.

Depending on the belief system itself, the actual claim "there is no god" COULD be a faith based claim, or it COULD be an evidence based claim depending on what the assumptions of the belief system are - I am voting "yes" only because at some level it does require a faith based set of "first principles".

So to whether "atheism" is a religion, I'd have to say that no, atheism per se is not a religion, just like theism is not per se a religion. Christianity is an organized movement which has theism as a central tenant, so I would say Christianity is a religion. Similarly, a group such as "American Atheists" is organized around the central tenant of "atheism", I would also consider a religion, although a group organized around the non-existence of god.