I think we will be seeing a mash-up of Ultimate Avengers 1 and 2.
What we know is that there could be a very high chance of the Hulk being a villain, as Banner found a way to control it at the end of 'The Incredible Hulk' and how Stark went to the bar to speak to General Ross about the "team".
And we also know that Tom Hiddleston has been signed on for 'Thor' and 'The Avengers', as well as Tim Roth being signed on for three more films after the release of 'TIH':
Tim Roth, who played Emil Blonsky/The Abomination in last year's The Incredible Hulk, confirmed that Marvel has made overtures to him about reprising the role in future movies, possibly including the upcoming Avengers film.
"They have, but in a very different way," Roth said in a group interview at the Television Critics Association summer press tour Thursday in Pasadena, Calif., where he was promoting his Fox series Lie to Me. "I don't want to get into it, but they signed me up for three [films]."
Could that include two more Hulks, one Avengers and one Hulk or just two Avengers?
"It could be anything," Roth said in response.
I could very well see the beginning part of the film be the united Avengers searching for Hulk, as I assume that Fury is actually trying to get the Super-Soldier program back up and running, for future battles(maybe an impending alien attack for a sequel or just as a hint), and once they finally bring a stable Hulk back, we get a version of the Liberators, lead by Loki, with The Abomination, and whoever else they decide to bring in(my money is for Red Skull if he's used in 'Captain America' and possibly Justin Hammer from 'Iron Man 2' as I think Whiplash will end up dying in 'IM2').
And for a sequel, I think we should get an Ant-Man film before 'Avengers 2' so we can get in Pym, who then builds Ultron.
And I would also like a Ultron and Mandarin team-up, with possibly Loki again, as a Masters of Evil for 'Avengers 2'.
There could be so many possibilities though; hopefully no one screws this up.
And also, ThatDamnNinja, I think we will be seeing an 'Incredible Hulk 2' just because we all think Norton is not coming back, but he never really said he wasn't. I just wouldn't be surprised if the next film is in five or six years.