Friday the 13th isn't just a day to release terribad movies. It's also the perfect opportunity to promote zombie video games and Valve is doing just that by offering Left 4 Dead for half off the normal retail price on Steam.

This weekend, purchasing the zombie co-op shooter through the digital games service will cost you $24.99 instead of $50. Add to that the fact that free DLC is on the way this Spring and you've got a bargain on your hands.

If you want Blend Games' full pitch on why you should buy this game, check out our review. Trust us, you won't be disappointed. Even if you are, at least your disappointment was half-priced.