While the Steam Summer Sale may have commenced, you should probably claim one game for the price of absolutely free. Zombie co-op FPS Killing Floor is now available for free from the Humble Store for a very limited time- just two days. You can claim a download link here. You will be redeeming the game as a Steam key.
Humble has always been offering good games for its limited time deals, but this time it also serves to remind us that their store is also having a sale. Should you wish to pick up DRM-free games this is the best time to browse the store and have a look.