Valve is holding its Autumn Sale, throwing a bunch of games on special. Currently, you can pick up games like Dead Island for $4.99, which is a huge 75% off its usual price of $19.99.
If you haven't picked up System Shock 2 yet (what's wrong with you?!) it's up for sale for just $2.49, down from $9.99. Killing Floor is also 75% off, down from $19.99 to $4.99. If you want to pick up some games, you should keep checking these Autumn Sales out. There'll be some new games discounted in around 18 hours time.