What exactly are you trying to do? A one on one conversion/ brainwashing, or a mass charm? Diplomacy is used for the personal touch, in depth appeals, the Oratory almost works like a bard thing, appeal to the masses, but hardly any lasting effects unless applied multiple times.
Oh, and for the things like Clerics, I liked that pic that was done by Lord Geryon, the one of Darth Vader and the words. "I find your lack of Faith.. Disturbing.. "