I am thinking that although George Lucas stated that there would be no third trilogy, he will definitely change his mind. He may not be quite as involved, but like ExistentialDisorder says, he's not gonna let the empire die now.
There are some signs in the movies, for example, if the prophesy was that Annikin would bring balance to the force, and it seems he has, at the end of ROTJ, then who is on the Dark Side? The only two people left with the force are Luke and Leia. Is it Leia, Luke, or did the Emperor not die? Keeping in mind that lots of characters have fallen down shafts and lived to tell the tale (even with big explosions at the bottom). I have heard that some books have Luke or Leia turn to the Dark Side, but I don't read those non-canon books. How can there be balance if there is no evil Jedi? Even if the Emperor is dead, then why couldn't the Force just parthogenetically create a new Sith?
And (spoiler) if Yoda is having visions of Qui-Gon, why does he not appear to Luke with Annikin and Obi Wan? (other than the character didn't exist at the time of ROTJ). Is it that the ability to appear to living Jedi can only work with someone who has a connection to the dead Jedi's? This sounded to me like a way to work Liam Neeson into something, rather than a brief explanation of Luke's visions. Could be wrong tho.
I'm thinking that after the rerelease (starting 2007), Episode VII will be announced and be on the screen three years later.