Udyr, Zilean, Kayle, Talon, Karma, Alistar, Soraka, Vayne, Wukong, Karthus, Lee Sin, Gankplank, Pantheon, Tristana, and Sivir off the top of my head.
I'm not saying all of the above are OP, but they are extremely good and can be considered ban worthy. A good player playing any of the above champs will make your life hell.
I never thought Kog was ban worthy. Assassins > Kog. It doesn't help that the majority of the people that play Dominion build him wrong.
Also, I don't think Jax is worth a ban anymore. After the Gunblade nerf and the removal of the dodge mastery, he isn't nearly as strong as he use to be.