personally i think the two best villains to go with the new film would be the Riddler and Catwoman. Nolan has created a new realistic Gotham and to introduce super-powered villains would ruin the trilogy. characters like Mr. Freeze, Poison Ivy, Bane, Mad Hatter, Killer Croc and so on would place the movies back in the Tim Burton era and I'm sure we'd all glad we escaped that realm and hope never to return. Nolan should try and incorporate villains like the Penguin or the Red Hood. (of course since the joker doesn't seem likely to return i suppose he couldn't do Red Hood.) or even Hush could keep the dark knight essence to the story. if you agree or disagree please leave a comment below.

I think Bane could be done very realistically. If you do some research on power lifters in prison you'll see that there are guys who can lift up to 600 pounds. Just imagine if one of those guys used steroids! Now obviously the whole tube delivery system would have to go (which it basically has for him since the no man's land arc) but if Bane was an escaped convict power lifter on major roids who took false adrenaline before fights (just so we could have a nod to the characters roots) he'd be a major threat and not a far stretch from the imagination. I think a Riddler and Bane (with Bane being of average intelligence able to maniuplate bats but not find out who he is) team up for the next movie would be awesome. Because imo we haven't gotten to see this Batman pushed to his mental and physical limits, imagine how damn cool it'd be to see both at once!

I second Bane.  It would be great for Batman to have a real physical challenge and I think it is something Chris Nolan would relish.  I don't think Batman's physical prowess has been fully explored.  They were doing so with Ras but I think we need to see more of this side of Batman.  My favourite fight so far has to be Batman and Ras at the end of Batman Begins.   TDK was a slight let down (don't shoot me please) in the combat department.
 
I really wonder how the whole Catwoman thing would plan out.  I am not as enthusiaistic as many are on here about Catwoman's potential inclusion.  I just hope any - and somewhat inevitable - romance element would not ruin the story line like it did with Spider-man (for me anyway). 
 
Jonathan Nolan has already said there will be no Mr. Freeze and I really don't see Poison Ivy or Killer Croc fitting into Nolan's world. 
 
By the way OP I agree with your suggestion of Hush: he has that sinister presence about him.  We know Nolan likes to adopt parts of the comics so a Riddler / Hush combination would be good.  Sorry to sound pedantic OP but do you not mean Joel Schumacher instead of Burton?

" I think Bane could be done very realistically. If you do some research on power lifters in prison you'll see that there are guys who can lift up to 600 pounds. Just imagine if one of those guys used steroids! Now obviously the whole tube delivery system would have to go (which it basically has for him since the no man's land arc) but if Bane was an escaped convict power lifter on major roids who took false adrenaline before fights (just so we could have a nod to the characters roots) he'd be a major threat and not a far stretch from the imagination. I think a Riddler and Bane (with Bane being of average intelligence able to maniuplate bats but not find out who he is) team up for the next movie would be awesome. Because imo we haven't gotten to see this Batman pushed to his mental and physical limits, imagine how damn cool it'd be to see both at once! "

I Want Jervis Tetch as a Side Villain, if that's not asking too much... Or hell, even The Ventriloquist + Scarface, Even if they only get a Cameo like Zsasz did...

i think that like the first 2 films there should be 2 villains
In Batman Begins:  Ra's al Ghul and  Scarecrow
In Dark Knight:  The Joker and Two-Face
In the 3rd movie:  Hush or Black Mask and Bane

I think the riddler could be done in a cool dark way. Not clad in question mark spandex rather an anarchist playing a game that centres around batman. I mean the only thing that is really needed is riddles. You couldn't possibly call him edward enigma and maybe just have him known as nothing other than riddler same way joker was never identified.

Mad Hatter and Riddler, i hate Tim Burton universe, it was a generic Tim Burton movie.

After reading the Jokers Asylum Killer Croc issue, I found a special place in my heart for Croc. I would like to see him, but I doubt they would bring him in. I think Hush is more likely to appear.

I would love a combination of strong and psychotic villains.For strength I prefer Bane or Killer Croc.For something darker I prefer Hush,Hugo Strange or Mr. Pyg (WTF????) !!!I It would great to see Batman doing investigations,like a detective to find a crazy killer.Also there has to be a love interest,Catwoman or Talia Al Ghul (she could take revenge for her father).

" After reading the Jokers Asylum Killer Croc issue, I found a special place in my heart for Croc. I would like to see him, but I doubt they would bring him in. I think Hush is more likely to appear. "