Digi-download service Steam is currently hosting a whopper of a sale, with prices slahed across the board until January 3. If you get a PC for Christmas, get yourself on Steam pronto.
There are daily offers and new offers appearing all the time, so set Steam as your homepage over the festive period.
Mirror's Edge, STALKER, Flashpoint, GTA IV and literally hundreds more are up there with 75 percent off. Madness. You'd be a fool (or an Xbox, PS3 gamer) to not be interested.