Just prior to the Summer sale, Valve released Team Fortress as free to play! Personally, I haven't played it since they started the store for the silly looking hats.
Now that TF2 is free, what does that do to the price of the Orange Box? Previously it could be purchased for about $20, but we'll have to see what happens now that one of the major components is free. Speaking of the Orange Box, another included game Portal, has a successor - Portal 2 - that is on sale in the Steam Summer sale. It's over 30% off at the moment. I don't expect it to be any lower during this sale, but can probably be bought for about half-price by the Christmas sale.