As most of the living know, Bungie have a new game (or 2) lined up which was supposed to be announced at E3, however, due to a "full schedule" as Microsoft put it, it didn't come to pass. The next big expo is PAX 2008 (Penny Arcade Expo) which starts August 29th - 31st and Bungie have always been a prominent exhibitor. If the rumours are true and the upcoming title falls into the platformer genre, this could be the perfect place to introduce it to the world.
Bungie's latest news insert tells us that they will be showing some new multiplayer content for Halo 3 at PAX. It will be interesting to see what extra content will be available for the current top xbox live game. (Yes, you read that right, Halo 3 is back to the top of the leaderboard as the most played game on Xbox Live.)
If the new Halo 3 content is the only excitement at the PAX Expo, this leaves the Leipzig Games Convention (August 20th - 24th), E4ALL (October 3rd - 5th) and The Tokyo Game Show (October 9th - 12th) as the other big events to make their announcement.