We have a pretty good idea who all the major players in Marvel's Phase 2 plans are, but we won't know everything for quite some time. Things don't really kick off until Iron Man 3 launches in May, so it's at best extremely premature to start speculating about Phase 3. There's already been some confirmation from Kevin Feige about Dr. Strange and Ant-Man, but now Latino Review has a major rumor that if true would blow the lid off the entire thing. Get ready for some possible major spoilers.
They say that at the end of The Avengers 2, the Hulk (Mark Ruffalo) will find himself stranded in deep space, setting up a potential solo film that would follow the popular Planet Hulk storyline. In that story, which was adapted into an animated feature a couple of years ago, the Hulk lands on a distant planet where he becomes a gladiator, ultimately forming his own team of slaves and taking the place over, becoming a king. Think Spartacus, only more green. It's also during this time that the Hulk has a son, Skaar.
So how does the Hulk end up in that situation to begin with? Apparently, Marvel is planning to create their own film version of the Illuminati. In the comics, the Illuminati is a secret group made up of the world's smartest men, including Reed Richards, Captain America, Dr. Strange, Black Panther, Namor, Tony Stark, and Black Bolt. They deem the Hulk too dangerous and arrange for him to be sent off into space. Of course, since Reed Richards, Xavier, and likely Namor are owned by other studios, they'd have to change the line-up considerably. Maybe they'd put Daredevil in there now that Marvel/Disney owns him again? Eh, maybe not.
All of this would conclude with The Avengers 3, when the Hulk returns to Earth looking for revenge and setting up a World War Hulk-style storyline where he battles his former friends.
I wasn't that big of a Planet Hulk fan, but World War Hulk was pretty awesome. Both would make for incredible live-action flicks. Of course, we're a long way away from ever getting any sort of confirmation. So just take this as a rumor and file it away somewhere.