Update - Official plot:
"After Independence Day redefined the event movie genre, the next epic chapter delivers global catastrophe on an unimaginable scale. Using recovered alien technology, the nations of Earth have collaborated on an immense defense program to protect the planet. But nothing can prepare us for the aliens’ advanced and unprecedented force. Only the ingenuity of a few brave men and women can bring our world back from the brink of extinction."
You may have thought that was it when Will Smith blew up the Alien mothership in the first Independence Day movie, but that's without taking into account Hollywood's inventiveness, especially Roland Emmerich's: He and Dean Devlin do have a few ideas for an Independence Day 2 movie!
Roland Emmerich is eager to develop this project, but he's encountering some surprising resistance from the studios who aren't as thrilled as us by a movie sequel to Independence Day... And that's not a rumor, it comes from Roland Emmerich's own words:
"Dean Devlin and I are still set to make a sequel likely because we've found some sort of idea and we approached FOX and FOX has not quite figured out how to incorporate Dean's and my deal, and Will Smith's deal. Will wants to do it in some sort of a package they can live with. So it's just been in negations now since forever, and naturally FOX says 'Why don't you do it without Will Smith?' I said Will is essential for us, for this movie and actually for the audience too. And, so, it's in limbo and lately the studios are fighting. Like gross players, and Will is a gross player and is probably the only gross player right now who's worth his gross. So we'll see what happens. I would love to do it."
Director Roland Emmerich
Roland Emmerich being both a business man and filmmaker I'm quite sure he will find out how to push forward with Independence Day 2. And if his script for the sequel is that good I bet Will Smith would not hesitate to get onboard.
But getting a good script may not be that easy: what could they possibly come up with? The alien mothership and its shuttles have been destroyed. Did a few alien manage go reach Earth's surface? Or is there a second wave of flying saucers from outer space with aliens coming to avenge their lost brothers and to feast on mankind?
Anyway, whatever the plot trick they will use to make Independence Day 2, I'm already sold! Bring it on! :)
Update - July 2012:
"I feel like we got it. I think it took a long time, but I feel like we finally got something that really feels like, that’s worth seeing as a sequel to Independence Day. [...] We’re beginning a long process of talking to everybody. We’ll just have to see what happens."