Portal 1 (Mac/PC) seems to be free for all till 09/20/11. Get it while it's hot. Steam is required though.
Already downloaded. Neat game.
While you are at it, don't forget Team Fortress 2 which was released as free for all a while ago. And for the next ~22 hours there seems to be a sale on Mirror's Edge for $5.00/£3.50/€2,50 .
This list might be also interesting to some.
Portal doesn't seem to be free here. Bummer!
Really ? Nothing happens if you click on the upper right logo? Or is it because you have a PPC Mac?
Don has his trusty g4, which the game doesnt like. 
Used to be into 3D shooters big time. Carpal tunnel took care of that. Gamers be careful!
Awesome game, already have it... with Portal 2 of course 8)