The Slut pointed me to Tektonics' satire Over Three Hundred Disproofs of God’s Existence. Norm Doering points us to Vox Day's call for arguments against Christianity.
But there really is only a single argument against the existence of God. To keep this from being my shortest philosophical post ever, let me relate to you an apocryphal story:
It's the final exam for Philosophy 101. The professor places a chair in front of the lecturn. On the board he writes, "Prove this chair does not exist."
The students all scribble away for two hours, presumably constructing edifices of careful philosophical reasoning. All but one. He thinks for a half an hour, puts pen to paper for less than ten seconds, and leaves triumphantly. He receives the only 'A'. His paper?
So my gentle (or "militant") atheist reader, the next time you're pressed for an argument proving that God does not exist, you may simply ask, "What God?" and walk away well-pleased.