This year's sale runs from December 19 to January 3 and as in previous iterations, it offers a wide swath of discounts. First, there are the daily discounts, which collect a handful of games and slash their prices. At the moment, you could pick up BioShock Infinite for $10 or Batman: Arkham Origins for $25.
Then there are the Flash sales, which usually offer larger discounts than the daily discounts, though they only appear for eight hours. Right now you could pick up Counter-Strike: Global Offensive for $3.74, but eight hours from now you'll be out of luck.
Not just a sale, Steam's holiday celebration is also a community event. Every eight hours three games will be offered up for the community to vote on. Whichever receives the most votes gets a deep, public discount. Voting also entitles you to one free Snow Globe card with which can unlock rare items in Steam games such as Dota 2 and Team Fortress 2. Or you could simply horde your cards until you have enough to craft the Snow Globe 2013 badge. This won't help you in-game, but it's a nice reminder of how you spent this year's holiday season.