If you are reading this, you are probably thinking "Oh crap, more fanfiction!". Obviously every fan boy is coming up with their own ideas for the next Bat film. Obviously Nolan is not going to every read some fanfic and say hey this is exactly what I'm going to base the next Batman film off of (If he ends up doing the next Batman film). BUT we do know that Nolan does want to please his fans to some extent. Obviously not mentioning villains for the next film at the end of TDK was to avoid bland constitency and to allow us fanboys to rant and rave on whats coming next.
So for the next film obviously they can not jump to far ahead. Batman is now a fugitive again and the public is out to get him. For the end of this trilogy they need a conclusion of Batman redeeming himself and being accepted as Gotham's Protector. The last two films in my opinion lacked one aspect of Batman, he is the World's Greatest Detective. None of this was ever really show in Begins or TDK. Batman in Nolan's Universe has been in the game for about a year or so. So the third film would be about a year and a half to two years, Batman should be well experienced by now and fully capable of showing his cunning and wits.
So obviously I truly believe that to make any good Comic film the villain needs to be the opposite of everything the hero is representing. So obviously Batman would be looking to keep cleaning the streets while avoiding capture, and hoping to be accepted by the public. He may not be actively seeking redemption since he did choose to take the blame for Harvey's murders. So Batman stands for acceptance/redemption in Gotham. The villain will need to stand for capturing and/or unmasking the fugitive Batman which would in turn counter-act everything Batman is trying to accomplish. The villain with the brains to do this would also have to become somewhat obsessed. The Riddler fits this description to the T. The Riddler physically can not compete with Batman but mentally is an equal therefore a battle of brains not brawn would follow.This is the stepping stone in proving Batman as the "World's Greatest Detective".
So lets eloborate of the Riddler's representation on film. He needs to be real-world esque. Obviously needs a little backstory can't just throw him out there like the Joker. Alot of people also think he is a poor-man's Joker so he needs to seperate himself from the Joker. I'm not a fan of tight wearing domino mask Riddler from the 60's TV show or portrayed by Jim Carey in Batman Forever. I've been more of a fan of the suit-wearing bowler hat Riddler in the animated series and comics. Last year a graphic novel was released called The Joker. The Riddler had a very small part in the book but, I loved how he was visually portrayed. Below is a few panels of him from the book.
So minus his limp, jeans, and red tennis shoes basically I love the look of this Riddler from the waist up. So instead have him walk upright, give him black slacks, and black dress shoes. Make his green coat a little longer and keep him shirtless underneath showing the awesome tats on his stomach. To go along with this look he needs to be mid 20ish. To go along with his brains have him be sort of a computer hacker. His crew younger also, less mob style more street gang, driving rice burners ect. So to pull off this look which actor could be used. Sure everyone rants and raves over Depp, but why have an older A-list actor when we can go with a younger actor with plenty of talent. I choose as the Riddler: Chad Lindberg. Yeah, the kid from the first Fast and Furious.
He can pull off the look and portray the smart, computer hacker type Riddler I'm envisioning. Grow his hair a tad longer and dye it a little red bingo!
So we have the villain, the look, and the actor. Whats left is motive and plot. Batman is eluding capture (thanks to a little help by Gordon) and bringing in whats left of organized crime. Since Joker overtook the city organized crime took a huge blow. The new DA wants Batman in custody and most of the police force makes it their sole priority for the death of their comrades. SO the Riddler's motive to solve the biggest riddle of all, finding out who the man who eludes capture from the police on a nightly basis and still brings in criminals to boot.
Obviously there needs to also be another villain. One to challenge Batman physically. The one peice missing from Bat's life is a love interest so introducing Selina Kyle/Catwoman seems logical. Someone to give way to Bruce getting over Rachel Dawes and challenge Batman in combat. As others have stated it would be stupid to go the innocent girl dies and gets ressurected route. Instead Catwoman needs to remain a jewel theif who's name comes from what she does: A female cat burgler.
An article by Soul-Eater regarding Catwoman describes her perfectly. In my version of the third Batman film this Catwoman is physically and visually would fit perfectly. If you would like to read this article here is the link:
http://www.comicbookmovie.com/fansites/HiveOfVillainy/news/?a=6040
So besides the entire storyline we have the basic premise. The villains, the looks, motives ect. Obviously Nolan can do a better job than any of us as to producing a story but, here I laid groundwork to the villains and their motives to giving a good opposite to Batman.