Mark Hamill has to drop some weight and finally portray the Joker in live-action!

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They kind of did that in the first one(original Michael Keaton film I  mean) a little bit, well the mobster part anyway..lol

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I don't see why people want to re-do the joker as a Heath Ledger style Joker. Admittedly I loved that performance, but one of the reasons I loved it so much, was because it was so different than the other portrayals of the Joker, while still capturing the fundamental aspects of his character. Personally, I think the next joker should go back to the classic Gwynplaine look, with perhaps a bit more unkemptness, but not to the point of TDK. The Joker Blog guy is a fine imitator of the Ledger Joker, but that doesn't work without the context of the previous joker incarnations. Now that that Joker style is well known amongst the populace, it loses it's power.

I feel the next Joker should be the new actor's, director's and writer's interpretation of the Joker. Not try to recreate Ledger's Joker, like nothing happened and nothing is different. Start a new, don't do an impression.
I don't feel it is disrespectful to Ledger or any one else to keep this decades old character that has evolved into a cultural icon a part of the movies. Jeremy Brett was a fantastic Sherlock Holmes. But his sad early death does not mean no one should ever play the master sleuth again, either.
Crispen Glover is just to frail and effeminate and not menacing enough to be Joker. At least not as I see Joker. Some people see him that way, I know. But Joker fights Batman hand to hand and wins as much as he loses. I loved it when Ledger's Joker gave him a good beating and hated it when Nicholson's Joker tried one punch and hurt his hand. Joker SHOULD be a psychical threat as well as his schemes and dramatics, other wise the fight is over as soon as Batman gets in arms reach.
It's getting so anyone with an angular, long face with sharp features and a wide smile gets suggested. Hell, by those standards Matthew McConaughey and Woodey Harrelson qualify, and I'd burn the world down first to save it from a redneck white trash Joker.
It's hard to define but Joker has to have a very distinct, cultured and dangerous EDGE to him. His voice and movement and vibe just need to creep out menace, seem to cut you. Even when he is just standing there. Like Tommy the Hitman once said of Joker. "He oozes poison. Turning the world toxic around him just by standing there. And he's pleased as punch to be doing it." So brilliant he's insane. I would have selected Willam DaFoe or Gary Oldman for Joker except they are already Goblin and Gordon, respectfully.
If you don't think Oldman would make a fantastic Joker, check out his performance in The Professional. His killing spree through the apartment to the tune of music only he could hear played in his head. He sudden decision to stop for no real reaosne except he got bored. The grin. The rapid violent mood swing.
Really, he was Joker-like in that film in many respects.  
A young Peter O Toole would be fantastic. But, you know, he is waaaay to old now but back in the day he would have been ideal. check out Night of The Generals and The Ruling Class to see him play insane killers who love to use a blade. Ruling Class is out there, but he is a lunatic who goes from thinking he is Jesus to thinking he is....someone else. 
I'm going to have to stick with DaFoe as my first choice. He's versatile enough to make his Joker different and yet authentic, and differentiate him from his Green Goblin.

I don't think anyone will read this but who I think should play the next Joker is Gregory P Loomis. Watch his YouTube videos of him reading the Joker's monologues, I promise it's good! He is a great actor and he is working on getting the role of the Joker. Personally, I like the idea of a sort of "nobody" coming and taking the role. Of course if a nobody came, the expectations and trust would incredibly high for him but I believe he can do it. If an already, well known actor came and played the Joker and completely bombed it, I'd probably move to another planet. There are very few actors that can compete with Heath Ledger and look like a Joker. When Jack Nicholson played the Joker, you didn't see the Joker you saw Jack. But when Heath Ledger played the Joker, you didn't see Heath you saw the Joker! If a celebrity played the Joker, their appearance might take over the Joker and we wouldn't see the Joker. Gregory P Loomis is who I think should be the next Joker.