First let me start by saying, if the riddler shows up in a nolan movie, I expect (hopefully) he'll undergo a "change" to a more realistic character, much like the Joker, Harvey Dent, Raz'a Gul (sp?) and even Batman himself did (and the result of that was amazing might I add).
That said, the new riddler would definitely be psychotic and obsessive compulsive, maybe even bordering the autistic (or asperger's syndome) with a very large IQ. He would lack self-confidence at heart, while, however, displaying a very confident and calm "cover".
We also have to factor in the performance of Ledger and Aaron Eckhart as Joker and Two-Faced (respectively) were nothing short of epic, you'd need actors to live up to their "legacy".
Such, I think the actors to best suit this character would be:
- Johny Depp - Because the man's a chameleon. Like, really... Go watch Pirates of the Caribbean, then watch Charlie and the Chocolate Factory and Sweetney Todd. Seriously, he can pull almost anything off.
- Hugh Laurie - Classic actor. Seeing him do Dr. House, then watching him as Captain James Biggs is quite surprising. He can convey emotions and he can convey mixed feelings.
- Timothy Olyphant - His performance in Die Hard 4 and in Hitman sold him for me. If someone can play a cold-hearted psychopath or an almost autistic-like persona full of mixed feelings, that's Olyphant.
Longshot: Keanu Reaves - I know. "WHAT THE FUCK? THE ONE-ROLE-MAN?". Well, truth is, Keanu has gotten better at his "ability to excel at one role but suck at everything else". I was pleasantly surprised with his performance in both Constantine and Street Kings. With Nolan's guidance, I seriously think he could pull it off, his innate "...what?" look could actually benefit his character.