I too had been thinking of what a Nolan Riddler would be like. To fit in the Nolan universe, I thought that perhaps E. Nigma could be a CSI Rock Star kind of guy. A guy who has been the king of his own little CSI-Gotham and he starts to get really jealous of the public acclaim that Batman gets for what he considers to "kindergarten sluething." To prove that Batman couldn't solve some of the tough cases he's had to solve, he would go back through his files and find the hardest ones, and then recreate them. At first, probably not by taking the lives of any new people... but as Batman IS able to solve the crimes, the Riddler escalates the complexity of the mysteries he expects Batman to solve.

Something like that. I'm not sure of the definitive origin of the Riddler, but I thought this one was probably "close enough" for a translation into the Nolan 'verse.

At the risk of Johnny Depp being in everything, I heard once that he was being looked at to play the Riddler and I thought he would fit the Nolan'verse pretty well.