Sound the alarms. Sound the klaxons. Snatch up your wallet.
It's a surprisingly convoluted sale. There are the daily deals, which already features Terraria and Total War: Shogun 2 at 75% off. Flash sales rotate every eight hours. The highlights of this current selection look to be Deus Ex: Human Revolution at a quarter of its normal price and the lovely, shiny platformer, Rayman Origins at half price. The first of looks to be a series of daily Indie Bundles is also live, offering Anomoly: Warzone Earth, Cave Story+, Edge, Lone Survivor and the Baconing for under £20 / $27.
Then there's the community slot, which lets everyone vote on a choice of upcoming discounts. The first choice: two thirds off Batman: Arkham City, Saints Row: The Third at 75% off and The Witcher 2 at 60% off. That is not an easy decision. If you're looking for something to play with friends, Saints Row's co-op mode is worth it at that price.
Then aside from those mini sales, there's a wide range of titles that are generally slightly cheaper than usual. If you're interested in playing DayZ, or love military shooters, Arma 2: Combined Operations is 20% discounted.
Also: BADGES. You can see your badge progress in a little section on the right hand side of your Steam community profile page. Clicking on that will show a series of tasks that you can complete to level up your Steam Summer Sale badge and earn a "Pillar of the Community" badge. There are bound to be rewards tied to these somehow, but we're not sure how that works just yet.