I'd love to see people's reactions to this, by the way. I might be too busy to react properly, but I'll try to answer questions, comments, complains, and arguments, whatever reaction you have to what I say.
I'm an atheist. What that means is that I don't believe that anything like a god is real. I'm not totally certain - I don't think any atheist is totally certain, however hyperbolic their rhetoric might become in the heat of debate - but I've thought about this quite a lot for quite a while, I've read a lot of arguments, and all told I simply don't believe it. I'm pretty sure that the people who do believe there are any gods, be it one, a few, or many, are simply mistaken.
I'm an atheist. I'm a strong atheist - I believe that no such thing as a god is real. Now, this distinction commonly causes semantic confusion: "I don't believe gods are real" doesn't mean "I believe gods are imaginary", never mind that I could state both truthfully; it's perfectly common for atheists to not believe that gods exist, while simultaneously not believing that gods don't exist. Such persons don't believe they have the evidence to commit either way on the question. I do.
I'm an atheist. I'm a metaphysical naturalist - I think the universe operates according to fundamentally non-mental principles. Richard Carrier defined supernaturalism well in an essay a couple years ago: supernatural things cannot be broken down into non-mental pieces. That makes no sense to me. Everything I have ever learned - my education in philosophy, in physics, in psychology, in mathematics, in computer science, in literature - has given me a strong instinct that somewhere at the base of it all are simple mathematical laws. I draw the comparison to Conway's Game of Life: the rules are basic and unbreakable, but through their implications on higher and higher levels of complexity in the world shaped as it is we find everything with which we are familiar.
I'm an atheist. I don't believe there's any overlord of the universe to dictate moral laws for us, nor any afterlife wherein our acts can be judged. Our morals are our own - earned in the struggles and victories of our ancestral species, forged on the anvil of a world which does not tell us what we should do, but merely referees. Our senses of beauty, of honor, of justice, of fairness, of charity, of love, of pride, of disgust ... every subjective experience we have is ours, proven on the steppes from which we came and coming together to create that which is us. To declare that this makes goodness into something meaningless is, if you'll forgive the rhyme, senseless - we're not stupid, and if we value goodness, that is meaning enough.
I'm an atheist. I am an atheist because I have the freedom to be thus - the freedom to learn, to decide, and to proclaim. I would not live where I was required to be thus by ignorance, deception, or coercion: to be an atheist freely is to be aware of the need for freedom. As Alfred Tarski is quoted to have said, "The sentence 'snow is white' is true if and only if snow is white" - and to be forced to believe that snow is white is to be coerced to believe, be that belief true or false. The only way to be free to believe truth is to be free to believe what one must on the strength of one's own judgement.
I'm an atheist. I care about being an atheist - I care about what I believe, and about being true to what I believe. I want to be treated decently and with respect. I want the people who disagree with me to listen to me - to trust my sincerity and my rationality - and when they argue with me, I want them to be sincere and rational in doing so. I want the arguments against me to stem from a fair and charitable reading of my sometimes-clumsy explanations - you can fight me, but fight the true implications of my world-view with the true implications of yours.