Steam has launched a big "Perils of Summer" sale, offering a big batch of games at a discount between now and July 4, including 33% off on a Valve Complete Pack, 66% off all Codemasters games, 33% off all Ubisoft games, 75% off on a 2K Complete Pack, 66% off all Atari games, 18% off on a Rockstar Collection, 25% off on a Square Enix Eidos Collector's Pack, and more. In addition to the ongoing sale items they will be offering a selection of titles for daily 24-hour specials. For today these include Killing Floor for 75% off, Counter-Strike- Source for 66% off, Overlord Complete Pack for 85% off, BioShock 2 for 50% off (including four-packs), Unreal Deal Pack for 66% off (or 50% off on any of the individual Unreal games), Trine for 80% off, and Aion Standard Edition for 50% off.