Heads up, if you like to buy your games from Steam, make sure you're checking it every day from now til 2nd Jan.
http://store.steampowered.com/If you were around for last year's Steam Christmas Sale, you'll know how this works. If not:
Every day from now til 2nd Jan, Steam will have games up on their site for ridiculous prices. It is not uncommon to see big name games show up for -75% or even -90% off. If a game you want shows up on the "daily deals" - buy it, it's the cheapest you'll see it during the sale.
Be wary of buying things in the publisher deals because although they are good prices, theres a chance the game will show up as a daily deal during the next couple of days. Obviously if a game hasn't shown up on the daily deals once we reach the last day of the sale, that's your last chance to get it at a reduced price.
EDIT: First day examples:
Todays Daily Deals
•Fear Complete Pack- 75% OFF
•F1 2010- 50% OFF
•Fallout GOTY- 33% OFF
•All Prince of Persia titles- 75% OFF
•Peggle Complete- 60% OFF
•Bad Company 2- 66% OFF
•Deus Ex pack- 85% OFF
•Lego Batman- 75% OFF
•Super Meat Boy- 75% OFF
•Titan Quest Gold- 75% OFF
•Portal= 75% OFF
•Oddbox=50% OFF
Packs for duration of sale
•Valve Complete- 86% OFF
•THQ-87% OFF
•Bethesda-55% OFF
•Mumbo Jumbo-83% OFF
•Square-88% OFF
•TellTale-62% OFF
•Paradox-86% OFF
•IC Complete- 87% OFF
•OddBox- 25% OFF after today
•2K-81% OFF
•Rockstar-71% OFF
•Meridian 4- 75% OFF
•Southpeak- 60% OFF