Yes'um, let's get the prominent details out to start. Iron Man is officially set to be a trilogy, with 2 set for a May 7th, 2010 release. Downey Jr. has signed a 4-picture deal with Marvel Studios that includes the first Iron Man, IM 2, IM 3, and the Avengers film which is set for a July 15th, 2011 release.
Favreau will be returning as director for Iron Man 2, and will be executive producer for the Avengers film. I'm not reading that he's set to direct Iron Man 3, I guess it's just implied he will?
Terrance Howard, who is shocked over the decision and denies it had to do with money, has been replaced by Don Cheadle in the role of James Rhodes, aka War Machine. Cheadle will be assuming the role for Iron Man 2 and Avengers. Gwyneth Paltrow is set to return for the sequel.
The current Avengers roster includes: Iron Man, Captain America, Hulk, Wasp, Giant Man, Hawkeye and Thor.
Marvel's current plan is to "introduce superhero characters via individual movies that lead up to the characters teaming up for Avengers." That sounds like a hell of a lot of movies to make before 2011. I really doubt that happening, thinking of the possibility of a Wasp movie...
With Downey Jr. playing Iron Man, it is unsure if Norton will be reprising his role as Hulk for the Avengers flick. His falling out with the studio over the final cut of his picture probably means he won't. Eva Longoria was seen leaving a Marvel building with an Avengers comic, and there was speculation she might play Wasp. Typical rumor mills were hinting at Brad Pitt and Leo DiCaprio for Captain America, which seems very unlikely.
But yeah, those are the juicy details. I'm looking foward more to the Avengers film than any of the Iron Man sequels. A chance to see all those badass superheroes in the same film sounds extremely unmissable. And as good as Cheadle is, I am disgusted with the removal of Terrance Howard. Bad call Marvel, bad call.