UPDATE: Marvel has officially announced that Edward Norton will not be playing Bruce Banner (aka Hulk) in The Avengers. From the set of Captain America: The First Avenger, Marvel's Kevin Feige had this to say (via HitFix):
"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."
See Elisabeth Rappe's original post below...
For two years, Edward Norton and Marvel have been dancing around whether or not he'll reprise his role as the Hulk in The Avengers. Norton has insisted he's simply waiting by the phone for Marvel to call him up, and that he was eager to return to the character, but nothing has ever happened.