From Valve:

Steam now offers two new information sources for gamers. A weekly top-ten list of game sales is now available each week, published via an RSS feed. The list is updated each Sunday morning and reports the previous week's top performers on the platform. In addition, the Steam web site now also lists all active discounts, right on the home page, so bargain shoppers no longer have to hunt through the Steam store to find out which games are on special. See the current specials list in the tabbed area on http://steampowered.com, and subscribe to the Weekly Top Sellers list at http://store.steampowered.com/feeds/weeklytopsellers.xml.

Personally I think they've done it the wrong way - I'd much rather have an RSS feed for the specials that I can keep an eye on - I'm much more likely to buy a game if I notice it in my RSS feed on special.