Steam is making ten games free this weekend as part of its aptly titled Free Weekend promotions. You'll have over 48 hours to play them, as they unlock 10am Pacific time on Thursday, October 16. After that you'll need to pay for them, with the promise of substantial discounts.
Here's the list:
Company of Heroes 2
XCOM: Enemy Unknown
I'm looking forward to trying out GRID 2. I already own Payday 2 (heist game) and XCOM: Enemy Unknown (turn-based strategy/90's nostalgia), so I can recommend trying those out too!
If you don't already have Steam, it's free to download. The website is http://store.steampowered.com/
If you try out Payday 2 for the weekend, let me know! My Steam username is Tohru Rokuno, and I would enjoy some multiplayer heists.