There are a number of villains to choose from,but only a few would fit into the Nolan universe.He may have to follow studio direction by choosing a villain who is well known,and marketable.
I do feel that Catwoman neeRAB to play a part in this movie.In my opinion,she is one of the most important elements to the whole Batman mythology.Also,there is more than enough material to work from,including backstories of Selina Kyle being an ex-protitute etc.The Riddler is probably the most apt villain,but the Batman/Catwoman relationship should probably take center stage.