If not believing in one particular thing is a religion in itself, I guess not only is atheism a religion, but so is, well, whatever you'd call a lack of belief in invisible pink moon unicorns. I guess we're all part of the same religion, then, given that probably none of us believe in those, so we can stop this debate.
[edit]
Okay, wait, I just saw ¿'s post and, unfortunately, am too taken in by the troll-bait:
Beat me to it. Atheism fits more or less in most of the definitions.–noun
1. a set of beliefs concerning the cause (Chance), nature (Of Chance), and purpose (None) of the universe, esp. when considered as the creation of a superhuman agency or agencies (Which there isn't), usually involving devotional and ritual observances (Avoidance thereof or you might consider their organized resistance to other religions to count), and often containing a moral code (There isn't an absolute moral code is the moral code) governing the conduct of human affairs.
Except "atheism" implies nothing about the actual cause, nature, or purpose of the universe, doesn't even say anything about supernatural entities or concepts which AREN'T gods (see: atheistic buddhism), doesn't have ritual observances at all (what the fuck makes you think that there are rituals related to not having a belief in some thing? do you have ritual observances related to your lack of belief in three-legged sloths?), and doesn't imply that there is or isn't an absolute (or any other) moral code in and of itself.
2. a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects (See #1)
It's more like a singular lack of belief, and if you take that to mean it's a religion, then sure, we ALL belong to an infinite number of religions, since we all share a lack of belief in an infinite number of things.
3. the body of persons adhering to a particular set of beliefs and practices (Like I said, when they become organized around a particular set of beliefs, it's a religion.)
Again. Being an atheist says nothing about the actual practices or beliefs you do have. People gathering because they're atheists is no more a religion than people gathering because they share any other trait in common.
6. something one believes in and follows devotedly; a point or matter of ethics or conscience (See this a lot in atheists, arguing their points in ethics.)
Atheism itself doesn't really make any points about anything. The biggest point it can ever make, itself, is a refutation of somebody ELSE'S point that God exists. That's all.
Atheism is a religion.
It's hard to believe you aren't being this ignorant on purpose. I have a feeling you're either trolling or simply are very, very ignorant of what atheism actually is or what atheists are like.