Actually, after seeing Episode II, Attack of the Clones, I have no idea what Lucas will name Episode III. The name "Attack of the Clones", despite it's B-Movie flavor, does not accurately convey the content of the film. A more fitting name would have been "The Clone Wars" or "Empire Rising" or "Splintered Republic" or something like that. The attack made by the clones was not the central premise of the movie. The central point was the conspiratorial splintering of the Republic causing additional "emergency" powers to be given to Chancellor Palpatine that he uses to create the Grand Army of the Republic made up of the clone warriors to fight the staged war between the Republic and the seperatists' droid armies. That, along with setting the scene for the fall of Anakin in Episode III (he's already falling, he can't marry Padme and remain in the Jedi Order - the conflict has been set for Episode III).
The actual use of the Clone warriors in a rescue operation and the pre-emptive strike on the Secessionist's droid army on Geonosis is not the central point of the movie. It was simply an initial demonstration of the power of the Clone armies that will spread through the galaxy to bring it under the tyrannical control of Palpatine/Sidius. The movie deserved a different, better name.
As for Episode III names that I think would make sense (who knows what Lucas will actually call it), I think it should be named in such a way that Episode IV's "A New Hope" makes sense. The title should convey the fall of the Republic, the fall of the Jedi (and their extermination), and the fall of Anakin. "Darkness Falls", "The Falls", "Descent into Darkness", I don't know - but you get my point I hope.