Wonder Woman's rogues gallery isn't that strong. There's Ares, of course, Circe — who headlined the singled best episode of Justice League Unlimited — and Cheetah, who's notable because she was on Superfriends.
Did any of them make it on to the 1970s TV show?
In any event, it's probably not crazy to think that Ares might show up in the film. The God of War has the potential to be a good antagonist and he was interesting in the parts of the Brian Azzarello/Cliff Chiang run I read. But according to Heroic Hollywood, he will indeed combat Wonder Woman … and Sean Bean is a top contender for the role. They also report that Eva Green is being looked at for Circe.
Rumor or not, both are fine choices. Heroic Hollywood warns that this is in no way a done deal. Their source could just be looking at a scratch paper of casting ideas, but I think they're wonderful speculation for a Friday afternoon.