Well, Sion is... oh wait. Oops. (Sion is one of my mains)
Anyway, it depends on how much time you want to put into your champion, as to which you should buy next. If you don't mind spending a while learning them, Gnar, lee sin, maokai and (maybe) rumble would be good, with pretty good results. Vi is an amazing counter to most top laners because of her armor-breaking abilities, but since you like jax and wukong, you may enjoy pantheon more. He is pretty dangerous, with a stun that jumps you to your enemy. If you didn't like renectan, aatrox, or tryndamere, you may not like darius so much either. Besides, he's kinda striaghtforward and boring. Just stack stack stack.. dunk. haven't heard much about jayce, didn't look up much about irelia.... riven could be good. She's varied from a lot of other tops and is really powerful, but it's hard to say if you'll like her or not.