Steam does significant sales frequently, this thread is for them. Post whatever you find that's worthy of a buy at the discount.
First Deal: http://store.steampowered.com/app/19900/
Far Cry 2 for $15, today only!
http://store.steampowered.com/app/19900/
Every indie game on Steam is discounted 10% to 33%. There are some true gems in there.