Official Portal 2 Website
Information about Valve's Portal 2, including trailers, screenshots and preorders. Portal 2 - Update. © 2011 Valve Corporation, all rights reserved.
Portal 2 - Wikipedia
Portal 2 is a puzzle-platform game developed by Valve. It was released in April 2011 for Windows, Mac OS X, Linux, PlayStation 3, and Xbox 360.
Portal 2 - Portal Wiki
Portal 2 is the sequel to the award winning and hugely successful Portal developed by Valve Corporation. It features a single-player story set after the events of Portal's story; and a brand-new Co-op game mode, featuring additional test chambers designed specifically for Co-operative play.