A few more categories, if you like:
Unconscious Atheists — like newborns, for example, who never had the chance to believe in a god.
Unaware Atheists — those pagans who have never heard of the concept of god.
Apathetic Atheists (or "Agnostics") — they have heard about the concept of the existence of a god, but since they have not seen any evidence, they just don't care.
Likeliness Atheists (or "Belief Atheists") — hold that the existence of god is a metaphysical concepts, it can't be refuted, but there is no evidence for it. Although they can't rule out the possibility of the existence of a god with absolute certainty, they hold that the existence of some metaphysical entity (like phlogiston or an invisible dragon) should be considered unlikely.
Positivistic Atheists — go a step further and insist that any metaphysical concept is nonsense, a waste of time, like juryjone said.
Strict Atheists (also "Hardcore Atheists", "Proof Atheists") — claim to be able to prove the nonexistence of any god. Such a proof might go like this, for example: any god who hasn't created time or who doesn't have a personality is not the true Scotsman. But an entity with a personality creating time (therefore not being affected by time in the first place) is a contradiction, since a personality can't be without wishes, and wishes can't be without future, and that proves that it is not logically possible for any god to exist. Or something like this.
I guess I am somewhere between Apathetic and Likeliness Atheism, although Strict Atheism also has a certain attraction.
I guess you will be able to invent more categories.