I would love to see a pure evil, and diabolical Joker on the big screen, if he is choosen next for the sequel. (I'd rather see other villian first.) But if they went with The Joker I like the look of him in the Batman Dead End Short Film:
I think that is a great look with the straight jacket, but eventually get him out of the straight jacket and into the famous purple attire, but not a bright purple, more of a dark purple. And of course he would have to be insanely funny, not too campy or over the top, but just insane to the point where your like whoa, and it sends shivers down your spine when your watching him on the screen.
I am not really sure who I would go with for an actor on The Joker, I will get back to you on that one.
Great official Joker thread by the way.