Halo 3 was suppoed to be the last game in the Halo trilogy but Microsoft surprised everyone by announcing Halo Reach at E3 2009. If that wasnt enough than Community and PR director of Bungie, Brian Jarrard recently told VideoGamer the following:
I wouldn’t confirm or deny at this point. We’re really excited to get Reach out the door. Beyond that, we’re not at liberty to say right now what’s next.
I think there’s a lot of work just to get Reach done between now and next fall. At that point anything’s possible. We’re going to keep looking at making the games we want to make. Maybe that’s Halo. Maybe it’s not. We’ll have to wait and see.