There are new deals every 12 hours and like every year the community picks which gets a bonus discount. Theres a new vote every 24 hours that are associated with these bonus discounts of the 3 titles so go and vote! Every vote gets you one trading card. "Steam Trading Cards are virtual cards, earned by buying and playing games on Steam, that can be crafted into badges that grant rewards. Collect a set of cards to earn items that help you customize your profile and show off your gameplay. " There is more information here: http://steamcommunity.com/tradingcards/faq/.
All the steam sales are also listed here: http://store.steampowered.com/search/?specials=1&os=win