Halo 3. You'll really want to make double sure that you do, because Bungie is hosting the "Bungie Vs. The World" playlist, putting forth its best and brightest to compete against the common folk. Oh, and should you best a Bungie team on this playlist, you will win a shiny new set of Recon armor.
Furthermore, Bungie will be revealing new info on some upcoming maps: Heretic, Citadel, and Longshore. As if that weren't enough, the Halo 3 render to video feature -- now called Bungie Pro Video -- will be revealed, and there's a new podcast with Firefly star (and ODST voice) Nathan Fillion(!). Keep your eyes on Bungie.net (and right here, of course) for more details.