The Steam Holiday Sale is on now on! Each day you will find large discounts on games and bundles as well as smaller savings for games on sale through the entire period (until January 1st). In addition to huge savings throughout the store, the 2011 sale features two special promotions that allow you to win like never before. Explanation please!
That's a lot of complicated text, I know. So you can see a diagrammatic version on the Steam Holiday Sale page. For your first objective (which is just viewing your inventory) you will receive a 25% off Valve coupon (as seen below).