A new teaser trailer put out by steam hints at the fact that Half Life 2 is coming out for Mac sooner rather than later. The trailer is a Half Life spoof of the 1984 Mac Super Bowl commercial promoting the up and coming release of Half Life 2 for Mac on the Steam.
9 to 5 Mac and Cult of Mac has said that the game will come out sometime today though I just checked Steam and I didn't see it just yet. What you can get right now is a cool game called Killing Floor, which is a Co-op Survival Horror game. It's kind of like Left for Dead in a lot of ways but a lot darker and more mutant like enemies. It's also %33 off today making it a $13.39 purchase and it normally sells for $19.99.
Steam has already rolled out Portal for Mac and with Half Life 2 seemingly right around the corner there are going to be a lot of very unproductive Mac users in the next couple of months.