Valve has launched `Steam for Linux Celebration Sale` and all the games available for Linux are now on sale. During this campaign, the discount ranges between -50% and -80%.
This means that you can get Serious Sam 3 with a -80% discount (5,59 €), Counter Strike: Source with -75% (3,74 €), Half Life with -75% (1,99 €), Trine 2 with -75% (2,79 €), Crusader Kings II with a -75% discount (9.99 €) and so on.
Furthermore, if you've installed Team Fortress 2 (free to play) on Linux, you'll get a free Tux in-game item.
The sale will end on February 21, 10 AM PST.
You'll find a complete list of games available in this Steam for Linux sale @ http://store.steampowered.com/sale/linux_release/
The reason for the sale is that Steam for Linux is now available in Ubuntu Software Center, for Ubuntu 12.10 and 12.04:
This also means that Steam for Linux is no longer considered beta software.