At 9:44 a.m. on March 5, 2010 Valve officially announced Portal 2 via Steam News with a release date in time for the holiday season. Apparently the game will have co-op and a host of new game mechanics. The game is expected to be released for both PC and Xbox360 (like its predecessor). Expect something showy at GDC. Not much other information is available as of yet, though GameInformer appears to have some exclusive access for their upcoming April issue.
Take a look at their Portal 2 cover over here [GameInformer April Cover Revealed]
We’ll keep you updated as more information becomes available.