The Steam client is officially out for Ubuntu and to celebrate all the games for Steam that work for Linux are 50-75% off. The Steam client for Ubuntu has been in beta for a few months and can now be found in the distros Software Center. This is great news for Linux gamers (or at least Ubuntu Linux gamers); right now the software library may not be anywhere near as comprehensive as its Windows counterpart, but that was also a similar story when Steam first launched on OS X. Since then many games were ported over to OS X thanks to there being a tried and trued time tested platform for them to be distributed on in the form of Steam.
For a long time Windows had been the singular choice for serious PC gamers with those on OS X getting a few games here and there depending on the developer or publisher, with Blizzard being one of the few to always release OS X versions of their hit titles. When Steam came to OS X it changed all of that and hopefully the release of Steam for Linux will do the same for that game fledgling platform. A majority of the games available for Linux via Steam have already been available for the platform previously outside of Steam, but notably now Source games, those that are made by Valve or utilize said Valve engine, will start to be available for Linux thanks to the company porting the entire engine over to Linux. Currently there is no official word if the software will be available for other distributions of Linux in the future.