Here's an idea I was toying around with, tell me what you guys think of it.
If Depp, or another youngerish actor gets cast as Riddler, what if the Riddler is portrayed like this:
Imagine a young businessman who suddenly takes the world by storm. He's making a killing in the stock markets, he's young, attractive, on top of the world. He's actually taking press away from Bruce Wayne. The guy's a complete charmer, a regular media darling.
Underneath it all, we realize he's a psychotic narcissist. He's funding and operating lots of black market schemes, and he's trying to gain control of the underworld at the same time he's trying to gain control of the buisness market. Bruce Wayne stands in his way of gaining control of the market, Batman stands in his way of the underworld.
So you have him frame Bruce Wayne for a murder, to try and force Bruce out of the way for him to grab his company, while at the same time forcing Bruce to go on the run. Now Bruce is in a whole lot of crap from both sides, on the run as Bats and Bruce Wayne. could do for an interesting dynamic.
Basically I kind of picture the Riddler as an anti-Bruce in this situation. A genius with an obsession, but this obsession is for power, not to help others, and his one weakness is his compulsion to leave behind riddles.