In addition to the usual savings specials, each day of the sale will feature a special Holiday Bonus on one select title. The twist: Players must qualify for the Holiday Bonus by owning another Steam game. 

For example, the first Holiday Bonus is Portal - save an extra 10% if you own Half-Life 2. If you already own the title, Steam will automatically detect this and offer you the 10% savings during check out.

Meanwhile, titles kicking off the traditional savings include:

• F1 2010                                 50%
• Battlefield Bad Company 2     66%
• Fallout 3 (Game of the Year)  33%
• The Deus Ex Collection          85%
• LEGO Batman                       75%
• Peggle & Peggle Nights          60%
• Prince of Persia (Franchise)    75%
• Portal                                     75%
• F.E.A.R. (Franchise)              75%
• Titan Quest Gold                    75%
• Super Meat Boy                     75%
• Oddworld's Oddboxx             50%