Riddler is on the casting brief, so I think it's a pretty sure thing he shows up in some regard. 
 
I think Catwoman is an obvious go-to in the Nolan universe, because she can so easily be an anti-anti-hero version of what he did for Bruce - a perfect complement, given how the last movie ended. However, of all the villains in the original quartet of Batman films, Selina Kyle is the one they did the best, so its a precarious challenge to take on, at best. 
 
It might be a fools errand or a jump-the-shark moment for Nolan. I think it partially depends on if he really wants to close his universe succinctly or if DC convinced him to leave it open for further reinterpretation (i.e., Catwoman is the latter, not the former).

What about Vicki Vale?! I think there should be 2 love interests though. Choose two out of Catwoman, Talia, and Vicki. Make it one of the conflicts Bruce has to deal with along with fighting whoever the villain is. And since every movie has 2 villains, they should just use Riddler and Catwoman and have Vicki Vale too. 
 
Also, the rumor I heard was that Selina Kyle (along with Dick Grayson) were going to appear but without being in their costumes. They're in it but not as Catwoman and Robin. But who knows?

After the death of Rachel Dawes, yes it's necessary.

Talia would be better, She should have appeared in the first film 

 a love interest of some sort might be important for the films to show that Bruce wont be forever upset about Rachel's death, not that he has grieved long enough, but to show that he will grieve.

I think they should bring in Ra's and the babe 
 
Batman: With a vengeance! :D

"No, but you know who is? Robin. "

"I prefer Talia. "

I don't mind Catwoman as long as she's not the main villain.

It all depends on the story done, if they need a love interest, if that love interest is Catwoman or Talia or someone else, it all comes down to the story.

"Catwoman is a tad too eccentric for Nolan's grittier, grounded interpretation of the Batman Mythos."

No Catwoman please. But having no love interest for Batman may be useful for the 3rd movie.  
 
During The Dark Knight, Rachel Dawes dies and Batman seeked revenge on the Joker. Then he is a vigilante by the end of the film.  
 
For the 3rd movie, Batman remains a vigilante and has a cold heart because of Rachel's death, so as a result, he is crueller to his enemies. That could work, right?

 
I don't see why she couldn't be in it, unless the only thing Nolan has seen of the character is the Catwoman movie.  
 
She is more realistic then half of Batman's villains, but I guess they could use anyone they want since they change them around a lot anyway. With that said, I think she could be as good as anyone else.

I think what made the dark night so good is the fact the ending was open ended.

i think selina kyle should be there, but not necessarily catwoman, maybe she should just be a thief

I think Nolan's Batman World is perfect (all puns intended) for Catwoman and where the Dark Knight ended, the story wrights it self; Batman meets the anti hero Catwoman. Flirt, mistrust, tracking the Riddler, all with Johnny Law chasing them all down. Open ending Batman saves the day choses being Batman over Selina, but still hope. Great Batman Movie

yes to catwoman no to Riddler. Talia would work better though with bookending the movies. But I Would much rather have catwoman. I really like that relationship. I really don't want Riddler in this. I would rather someone who would fit the batman on the run story like Hugo Strange.

I want villains we havent seen on the big screen. Put Hush and Talia al ghul in!!! even a legitimate version of Bane would please me.

Talia or Catwoman, can't go wrong with either.

Even black mask and the penguin having a gang war would be cool side story. 

I have to agree that you can't go wrong with Catwoman or Talia to provide a love interest. 
Much as I'd love to see Catwoman though, Talia would provide less of the cliche or deja-vu feeling.

Why can't we have, both?

From What I've read from Frank Miller Batman Begins first script was written by him and they later called in Nolan and Goyer to "write" the script. It just so happened that the new Batman script was very similar to the man who not only wrote Batman Year one but also wrote an early draft of the Script. I love the Dark Knight but I was not one of those who was in awe of Batman Begins. I kept thinking what would this have looked like if Frank Miller was involved in the writing? As for Catwoman..I wonder what a hyper realistic version of her would look like in a Nolan BatWorld? I think it would be best if he just stuck with one villain like the Riddler and make it a good puzzle solving story! (like a Red Dragon or Silence of the Lambs mystery). Let's put the Detective in the Dark Knight!

Catwoman would rock, but she should just be plain Selina Kyle for most of the movie. Do you guys think Harvey Dent is really dead? A PO'd Twoface would make a great villain. I hope Angelina Jolie isn't too old for Catwoman

Talia seems to be the good choice, but in all honesty a love interest can also emerge from Bruce's personal life as well since he is a billionaire playboy after all

I'd really actually prefer that Catwoman weren't in the next film, I'd much rather see an even darker vigilante Batman in the middle of a Gotham gang war between the Penguin and Black Mask. 

I don't care much for Talia, but you can't go wrong with Catwoman as long as she is kept too being a "thorn in his side" while he is attempting to take down the big evil he has himself preoccupied with her in both her identities.

In my idea, not that this post is about the love interests or Talia or Catwoman, but
in my idea the main villain (main focus like the Joker was) would be Riddler who would be this narcissistic type who has to show the police and Batman that he is the smartest by leaving notes, clues, riddles, and letters.  This would give Batman a chance to show he is more than a master fighter, and focus on his scientific/detective side.  The thing about the Riddler that could make him so dangerous is that he is as dangerous as the Joker, less chaotic, has more of a goal, and is much more intelligent.
Penguin would be a more human version (not the mutant like in Burton's) he would be an eccentric mobster taking over the crime world.  He is a sort of in between of the Falcones and the Jokers.  He isn't exactly a freak criminal like the Joker was, but he is more freak than Gotham's usual mobsters.  Showing the escalation, and the way things will be going.  His part would be as big as the mobsters in the Dark Knight.
Catwoman would be the sort of love interest.  She is a criminal, Batman hates criminals, but he is somehow unable to resist her even though he knows he should.  Her role would be like her role in Hush or the Nail.  And the size of her role would be like Rachel's in the Batman films.
Gordon, Alfred, and Fox's, roles would be as big as their roles in the other films.
 
So its reasonable to fit them all in, and still have a really good story that flows.

Honestly I'd like to see a serious take on a more cheesy villain like Mr. Freeze or Poison Ivy. We got a pretty darn good look at a serious Penguin and Catwoman in the second Batman film, but by the time we got to Freeze and Ivy it was just too clowny. Riddler and Two-Face were pushing it, but with Riddler in this movie we'll have both of them down for the count. So yeah...Freeze, Ivy...or Catwoman. I really don't think it'll matter if this is the last in the series.

I don't think she's necessary but she is an important character that many people, including myself, would love to see done right. 

I'd be fine with Catwoman. Honestly, I want to see what the Nolan version would be like. 
Talia perhaps makes more sense, but I admit I'd be more interested in seeing Selina. 

"Also, the rumor I heard was that Selina Kyle (along with Dick Grayson) were going to appear but without being in their costumes. They're in it but not as Catwoman and Robin. But who knows? "

Yes, they need to include Catwoman, because if the world truly is going to end in 2012, we need to ensure that the abomination with Halle Berry wasn't the character's final film appearance.

Animal totems, like Catwoman or the Penguin, seem like something Nolan wants to avoid.  He spent the whole first movie trying to explain how a bat costume wouldn't be totally ridiculous.  I don't think he would want to tackle it again in his attempts at realism in the future.  Talia seems like an interesting choice, but does every Batman film need a romantic interest?  He's not James Bond.  There is no need to have a token Bat-Babe, like there were in the Schumacher pictures. Whether or not there is a significant love interest in the plot all hinges on whether or not one can fit into the thematic thrust of the next film.  The one life line to Catwoman or Talia may now be that Batman in this next film is a wanted man, as of the end of the last film.  The whole public sees him as a monster.   With Catwoman or Talia's questionable sociopathology showing him the way, perhaps he will begin to think he is a beast and become one .

All I hope for really is please dont make Batman 3D.......... the whole concept is overrated and really oversaturated..  Catwoman might be ok for the movie , but she's like Robin in comparison i.m.o. Will we buy it? I would simply jump to Damian Wayne's mother instead. And for the main Villain I would put Deathstroke (Slade Wilson) as Batman's total opposite and Hush as Second Villain.

I'd prefer Talia myself. If only because she has a back-story relation to Begins on top of her introduction during the film.

I would absolutely love to have catwoman in the next movie. She is definitely the best choice for a new love interest.

Hush, Talia & some C-list villains (Deadshot for one).  Ya, that's the ticket...

I wanna see how Nolan would work Carwoman.
And someone's gotta redeem the Halle Berry travesty.

YES, she SHOULD appear, but she should NOT be played by Halle Berry!

The film is likely to be pretty damn amazing whoever they choose, I'm glad they never chose to do a 'bond girl' type thing with the Batman movies that would have sucked. I'm already counting down the days to the next Batman movie and I have no idea when it is :( I need a time-machine.