If you haven't played Portal 2 on PC, then you have no excuse -- none I tell you -- not to pick it up with a 75% price cut on Steam. Also on offer is Worms Revolution, which is free to play all weekend and half price to purchase. Valve is really spoiling us as it's got a third offer: puzzle platformer EDGE is half price this weekend too.
Amazon.com has a pair of contrasting deals this weekend: FIFA 13 is 75% off at just $9.99 and Empire: Total War - Gold Edition is half price at $19.99. GreenManGaming has 75% off the Grand Theft Auto franchise (though not Vice City, for some reason) and there's also 75% off a big selection of indie games too.
Over on GOG.com, you can get 85% off the recent Telltale Games episodic titles such as Back to the Future and Tales of Monkey Island. Over on Gamersgate, they've cut between 33% and 75% off the prices of the Assassin's Creed franchise. As always friends, leave any deals you find on PC deals in the comments and have a good weekend.