^^ Current Steam deals.
2 games for $15 at Get Games. Get it while it lasts here.
^^ Follow this flowchart above to get best deals. Applies to Steam only.
I'm too lazy to follow all the deals, so I'll just leave the links where you can find the best deals:
LEFT 4 DEAD 2 FREE ON STEAM in case you missed it.
Also, good article on Lifehacker how to get the best out of deals on Steam.
Plus, it would be awesome if you can post all the great deals you find here in the topic. I'll try that too.
Feel free to post XBL and PS+ deals here also.