Well the Riddler is probably the best known rogue after the Joker and Two-Face. DC probably figures that he would be more of an interesting character then the Penguin or Mr. Freeze. You may say Catwoman, but I think DC and WB still wants us to forget that abortion of a movie they put out with Halle Berry a few years ago.
Personally, I think this is there best option. Unless I am totally blanking on someone.