75% off sale + another 20% off with code BETATHANKS
I imagine that this is US only, or at least you'll need a US payment/address. I'm not 100% sure though.
These are good prices and probably the cheapest any of these games have been individually.
HL2 for $2, episodes for $1.59. $4 for the L4D games.
If you don't have Portal 2, $4 is the perfect price point.