Sharlto Copley
An amazing actor is an amazing actor, no matter who they play. Though most would never recognize Sharlto Copley in public, he is a remarkable actor with a massive scope and the true ability to chameleon every role he plays. Though perhaps most well known for his starring turn in the amazing District 9, there is much more to this South African actor than just slowly turning into a bug.
He actually has played batshit (see what I did there) insane villains in quite a few movies (Elysium, to name one), and I think he could bring elements to the Joker that some American actors would not be able to.
Hell, depending on which lore you follow, the Joker has a ton of different origins. How about giving us a Joker with an accent we cannot quite identify? Make him suave, yet always one inch away from snapping. It would a whole different direction for the villian, and I bet it would be awesome.