Crytek's Crysis and Crysis Warhead are infamous for pushing hardware to its limits even today, but they're also pretty swanky games once you get to play them. And despite their age, both have graphics that are still up there with (if not better than) some of the prettiest cross-platform titles.
If you've never given either game a stab, now's your chance: Valve is running a weekend promotion on Steam whereby Crysis and Crysis Warhead are available for $14.99 each.
You don't even need to buy both of 'em together—the deal lets you pick up either game for 15 bucks or the two for $29.98. Not bad considering both titles normally sell for $30 each. If you pick these up, just make sure you have a reasonably decent graphics card—at least something in the GeForce 8800 or Radeon HD 3800 series. Oh, and you'll need a good Internet connection, too, since Warhead alone is a 6GB download.