Anyone is fine with me, but when you look at it
Harley Quinn: This is the only villain I would definately not like to see, with or without the Joker. I just do noy understand her appeal at all.
Riddler: I feel I must agree with cjmcray on the Riddler, he is a watered down version of the Joker, but I do not see this as a reason to remove him completely, just give him a short scene like the Scarecrow in TDK to show the viewer that "the freaks are coming".
Penguin: Would'nt mind seeing him, maybe in a similar role to Sal Maroni, I can't see him taking the mantel of the main villain, not in Nolan's world. The problem is that most of the none comic readers are probably expecting him to appear as the lead, primarily because of the Burton movies people seem to think that: Joker = Greatest villain Penguin = Second Greatest villain, coupled with the fact that he appeared in so many episodes of the old 60's TV series, so Warner might put some preassure on Nolan to include him.
Black Mask: There are several reasons That this charecter is both unlikely and unappealing, they are not all imiediatly apparant.
Firstly his backstory is not that origional, one of the things which makes the Nolan movies is that they are unique, not just among batman interpratations, but among comic book movies in general. Black Mask's backstory is fairly overused among comic book movies, buissnessman owns large corperation, initiates new buissness venture, things go horriby wrong and he goes insane, becomes obbsessed with hero/hero's and tries to kill/destroy him/them. It would be Green Goblin and Doctor Doom all over again, just without Super Powers.
Also after the success of TDK over Batman Begins Warner may be trying to get bigger names in Batman's villains, ones whcih resonate with the none Comic readers, Black Mask does not do this in any capacity.
Mad Hatter: Same as the Riddler, he is what I call an "Er", villains who are basically watered down Joker's with slightly different motivations.
Catwoman: Has never been done justice on screen, there is no reason to think that will change now.
The Surreal Villains will definately pop up regardless of weather or not the franchise goes rebooted, and in a way I think it will be because of the third movie:
I think there will be no villain in the third movie, I think that is the way Nolan would want it, why? Simple most of the "realistic" villains are either watered down Joker's, have overused backstory's or just plain don't fit in.
Now I know most of you find the concept of
no villain 
unlikely and stupid but just hear me out...
As many have said before Heath's preformance is can't be topped, and another villain would be a step down.
But that is not the only reason, if it were than we could simply throw the focus back onto Batman, so you don't have to worry about the villains preformance.
But that is not the only problem here, the main problem is
Theme Nolan's universe needs a different
Theme for every movie. Without a relevant
Theme these movies mean nothing, if Nolan can't think up a
Theme he might as well quit or make the third movie fan service.
After seeing the end of TDK I have a pretty good idea of what the next theme is going to be, and I think ANY villain would just seem completely pointlessand out of place in it, like a pine tree in the middle of a desert.
What do I think the next theme will be? it'll be hard to sum up in one word...
The theme should be about who really has the right to defend Gotham, who has the moral entitlement to protect the citizens of Gotham. This was merely a side issue of the last two movies, however it is time to make it a full-blown theme, nope, theres no way around it now, Batman is being hunted by the Police, they and the many corrupt cops among them are the villains now. Lets face it, if it were not for the Police Dr Crane would never have been able to pollute the water supply, Harvey Dent would never have became Two-Face, Rachel would never have died, the Joker would never have gotten into the fundraiser and it is heavily hinted that it was a corrupt individual who put acid in Loab's drink.
It is time that we see Batman take on this corruption full bore, as he soon finds his efforts to defend himself from the police are spiraling to into a full blown war with Gotham's "Other" heroes, Batman also learns the true extent of the corruption and how much of a threat it really is to the chances of cleaning up Gotham and decides to eradicate it once and for all. This would make for a fascinateing story which the presence of a "Villain" would only detract from. The real villain would be the Police force, there would just be no need for an idividual villain, it would just seem out of place with such a theme.
So in short:
No Villain At All Please!