Hitman Absolution is currently 66% off on GMG, the game activates on Steam just fine and is for almost $17.
Swords and Soldiers is on deal right now on GMG for only $2.49 – the game is redeemable on Steam.
Warhammer 40,000: Space Marine is also on deal for only 5€ or £5 on GamersGate. The game uses Steamworks and is Steam redeemable.
And the last one for the day is Super Meat Boy on Steam for only 3,50€. If you are suicidal do not buy this game because you will jump.