I think the next big casting decision is DA Harvey Dent. Is it too late for Billy Dee Williams?
Edit: Actually, I have some people in mind:
Anthony Montgomery, a.k.a. Ensign Mayweather from Enterprise. He's a relative unknown, he can act, and he can play Dent to a T.
Adrian Lester, from Hustle, Primary Colrs, etc. Damn good actor, might be able to do evil.
Don Cheadle, arguabally one of the best actors in history (at least in my mind). He can do serious drama and serious action. Probably my #1 pick.