In talking with MTV, Kevin Feige even went as far as to tease a live-action Planet Hulk (which was turned into an animated feature in 2010).
Do I think Hulk can carry a movie and be as entertaining as he was in Marvel's The Avengers? I do believe that. I do believe he absolutely could. We certainly are not even going to attempt that until The Avengers 2. So there's a lot of time to think about it.
Part of what's fun about the way we played him in Marvel's The Avengers is the ensemble quality of it. I think the pathos and humor showcased a different element of Hulk that's there in the comics, and was always inherent in his character. But when he was so brooding in his other two films, he didn't get to have that wry sense of humor."
So, there you have it. According to Kevin Feige, there won't be another stand-alone Hulk until at least 2017 (yes, that's right, you do the math).