Just as expected, Steam's autumn sale kicked off today. It will run through Monday, November 26, and as always each day brings a fresh set of daily discounts and flash deals for the duration of the sale.
Today on the Steam Store you can snag on-the-cheap sales for XCOM: Enemy Unknown ($33.49), Magic 2013 ($4.99), Darksiders 2 ($16.99), Age of Empires 3 Complete ($9.99), Terraria ($3.39), and The Walking Dead Season One ($12.49, and highly recommended). Several revolving flash deals and indie games are on sale as well.
If any sales catch your fancy, be sure to grab them sooner rather than later. The deals rotate daily, and the flash deals rotate even more frequently, so it's best to jump on a price while it's still available.