Just a couple of minutes ago the countdown on Bungie.net reached zero, and a teaser trailer for their next game went up. No title has been announced, but the trailer is described as a new campaign experience for Halo 3. The trailer shows a city, crushed by a surprise attack from above - that is all that was shown.
The trailer ended with the words; "Halo 3", "Prepare to drop", "Bungie", and "Microsoft Game Studios".
"High action and deep mystery await players in this new halo 3 campaign experience. Prepare to drop!" - this is the description of the trailer on Xbox Live Marketplace.