As has already been mentioned, there seems to be as many defintions of the words "atheist" and "agnostic" as there are atheists and agnostics.
If someone were to ask me, do you believe in the existance of any god, I'd say no... and to me, this makes me an atheist.
In most cases I've found that the word "agnostic" to a lot of people is connected to somehow admitting that believing in god and not believing in god is in some way both equally valid stances on the issue... a 50/50 deal. While this is hardly the useage of the word "agnostic" you find in a dictionary (or on this board for that matter), this is how I've seen the word used most in everyday life, and therefore, I don't like the idea of using the word to describe my stance on god. I simply don't want people to associate me with that sort of wishy-washy stance.
I'd like to say though, that I don't in any way consider the issue closed. I don't believe in god, nor do I belive in invisible untouchable dragons, but if there is new and compelling positive evidence that imply otherwise, I'd gladly reconsider both my stance on the existance of god and the existance of invisible untouchable dragons.