I'm hoping more for Johnny Depp to play Joker in the future... as long as he doesn't play him as Jack Sparrow. Give him a fresh feeling, but still stay true to Heath's Joker. I think Depp has the capability. And no, I'm not one of those Depp-fans who cast him for everything. I avoid casting him in my mind for anything unless he's a "duh-yes!". And no, don't confuse "duh-yes" with "obvious-choice"... everybody thinks Depp deserves to play everyone: not true. But I do think he's a duh-yes for Joker.
http://cdn.buzznet.com/media-cdn/jj1/headlines/2008/01/johnny-depp-heath-ledger.jpg
Left: Johnny Depp (obvious)
Right: Heath Ledger (not so obvious)
The right picture, at first, I thought was Depp, but later realized it was Ledger. Depp has the look, and as you all know, the makeup almost completely hid Ledger's true face! Take someone who looks similar to him (Depp) and put the makeup on and you have a winner! Now all that's left is the acting... Johnny is capable, as long as Nolan reminds him "don't Sparrow-fy him!" If he doesn't do this, he can definatly pull it off! And as for the voice, Heath's normal voice and Depp's normal voice are slightly similar. Depp's is deeper, but Heath's has more of an accent (duh). Depp, I believe can pull off the Joker-sound. Hey, I can, and my voice is deep, and I'm not that good of a voice actor. If I can do he, Depp sure can.
There's only one person on this Earth I'd personally trust the character of Joker with at this point, after Heath's death and that's Depp. And obviously Joker MUST be brought back in. One movie in a series is not enough for Batman's most famous rogue. After Joker there's only so far you can go to draw mainstream interest. Riddler, on the other hand, I'd trust him with a whole array of actors, including Depp. But why cast Depp as Riddler (who you can cast someone else for) when Depp's so perfect for Joker!?
This "Heath-only" mentality has got to go... Most everyone doubted Heath (including me)... he gave no fore-evidence that he can play someone as cookey as Joker, but yet he pulled him off perfectly... Depp, on the other hand, has given plenty of evidence that he play someone cookey, but yet we doubt him because now, after seeing Heath, we only trust him. It was similar when only Jack was the Joker... About 60 percent of every Batman fan (guess-work) said "Jack-only!", but now look at what's happened. Heath has pwned Jack. Heath is not the only man in the world that can play Joker. Depp can. Maybe not as good. Maybe better. Point is, if Joker is to return (which is very much needed), Depp's Nolan's man!