Frictional Games And the developers TheChineseRoom announced the release date for Amnesia: A Machine for Pigs. If you preorder the game you can save 20% of the regular price.
Deep Silver announced that Metro: Last Light will be ported to Mac OSX and Linux. The Mac port is available at September, 10th on Steam. 4A Games is currently working on the Linux port which will be made available for Steam users later this year.
So in the meantime several games have been gone gold for Linux, e.g. HL2 and its addons like Episode 1 and 2.
The HL1 SDK has been updated so that it is now available for Linux and OSX.
The strategy game Warland: Airgame Battle is also available for Linux users.
Natural Selection 2 is available for Linux users.