Friendly reminder: it has begun

http://store.steampowered.com/

21 Dec - 4 Jan

Bonus: https://isthereanydeal.com/

Good year round. Useful to check where to find the best price for a game you want. And if you make an account and make a wishlist, you can get notifications when games reach a certain price or sale % (which you set, so no pointless notifications for a mere 10% "sale").