I've heard news that Gearbox is going to make halo 4. I think it would be interesting if the planet was a Flood research world by the Forerunners, or possibly the Sangheili home world.
the ending after you beat the game on legendary,after the credits hints towards a halo 4,but I say lets find out.It's pretty much the game Bungie is known for in our time.Whatever they choose to do I'm looking forward to seeing what happens.I wouldn't mind a Halo 4 and thought that while the story mode for Halo 3 didn't seem like it had enough emphasis put on it,because of how short it was,but the multiplayer was and still is some of the best out there in my opinion,and unlike in movies with games they can make the sequels better with everyone(its possible) now I say lets just watch.Its typically a matter on whether or not they can come up with anything to do with the sequel,the demand for a sequel, and other things like whether they want to make a sequel and other things I probably couldn't factor in.I think there is a chance that we could see a Halo 4 overall though.
OK there will be a Halo 3 ODST, its a campaign expansion to Halo 3. As for Halo Wars, Bungie just felt like making a different game with a different genre. This game will be available March 3 of 09. As for Halo 3 ODST that game is released some time Fall of 09. As for Halo 4 no one but Bungie has the right to say if there will be a sequel or not. Just watch the Halo 3 alternate ending, that might answer your question. I really hope there will be a sequel. Hopefully in Halo Wars or Halo 3 ODST there is some kind of message or clip that will let us know whether there will be a sequel.