Other possibilities:
-"Gods" are really manifestations of social belief. Their existence is only proof that the ability to work magic exists, to a greater or lesser degree, in all sentient beings; they represent a collective magical work. (sociological atheism)
-There are no gods, but magic itself is flexible. Some people channel their power through arcane words, whereas others channel it through prayer. Presumably, a magically-inclined person who believed hard enough could channel their magic through tap-dancing. Oh yeah -- that's a bard! (scientific atheism)
-I don't care what you say, the idea of Gods is dumb. (insane atheism)
-Gods exist, but they must be opposed at every turn. They are selfish powerful alien beings who treat mortals like expendable pawns in their internecine squabbles. Humanity will only be free once the Gods are driven out of our reality. (this might be classified as antitheism, rather than atheism)
Obviously, the available variants of atheism will depend on the world in question. A world in which the Gods make regular appearances won't really allow for what I'm calling scientific atheism. A world in which the Gods are very remote and uninvolved in human affairs won't have much for an antitheist to rebel against.
I tell players in my game that, while atheism is an option, it should be extremely rare, and will be regarded as an almost criminal insanity by most people. This is just a quirk of my world, though: it's easy to imagine a world in which atheism is a viable option for whole communities.
Daniel
