Edward Norton won't play the Hulk in the Avengers film

...cause he's not a team player (much like the comic book Hulk in the Avengers!) According to Marvel Films:

We have made the decision to not bring Ed Norton back to portray the title role of Bruce Banner in the Avengers. Our decision is definitely not one based on monetary factors, but instead rooted in the need for an actor who embodies the creativity and collaborative spirit of our other talented cast members. The Avengers demands players who thrive working as part of an ensemble, as evidenced by Robert, Chris H, Chris E, Sam, Scarlett, and all of our talented casts. We are looking to announce a name actor who fulfills these requirements, and is passionate about the iconic role in the coming weeks.”