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).
"I don't think there's a lot that we couldn't do someday, as the cinematic universe continues to grow and expand and get as big as the comic book universe. Planet Hulk is a cool story. World War Hulk is a cool story. I think there are pitfalls of continuity-overload, and mythology getting so dense that it almost collapses in on itself. It happens every few decades or so in the comics. Apart from that, I'd say everything is on the table.
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).