A while back it was rumored that Marvel Studios was planning on a "Planet Hulk" movie.
It was said to be a major scoop, but has since been shot down many times by the simple fact that Banner is not present in the storyline.
Now Mark Ruffalo says more of the same as he tells MTV the following:
"'Planet Hulk?' I don't think that's the way to go yet," he said. "I think you need more Banner. The whole thing is just him as Hulk, on a planet, fighting other gladiators."
The comic book storyline sees a group of superheroes trick the Hulk into getting sent to space where the Hulk is supposed to go to this planet that is a paradise (i.e. a place he won't be bothered). Instead, the Hulk gets sent through a worm hole to planet Sakaar, where the Hulk is enslaved and forced to fight gladiator-style in an arena.
Long story short, the Hulk eventually escapes and heads back to Earth seeking revenge on the heroes, in what is known in the comics as "World War Hulk."
Fun fact: Marvel had to replace Silver Surfer in the movie because Fox owns the film rights to the character. Beta Ray Bill was used in Surfer's place.