Atheism and agnosticism are not mutually exclusive terms. Contrary to popular belief, agnosticism is not this happy intellectual middle ground. If you don't believe in gods, you are an atheist. Period. Atheism and theism refer to what you believe, and gnosticsim and agnosticism refer to what you know.
There is a great explanation of this here:
http://wiki.ironchariots.org/index.php?title=Atheist_vs._agnosticSorry, I know it is knitpicking, but it just annoys me to no end when people who, by definition are atheist, try to avoid the label due to the stigma that theists have placed on it.
I am an atheist and damned proud of it.