Steam is having 50% off today

Half-Life 2 $4.99 (Got it)
Half-Life 2: Episode 1 $3.99 (Got it)
Half-Life 2: Episode 2 $3.99 (Thinking)
Counter-Strike $4.99 (Not getting)
Counter Strike: Source $9.99 (Got it) Once you got CS:S no need for CS
Day of Defeat: Source $4.99 (Got it) Came with CS:S
Left4Dead $9.99 (Not getting)
Left4Dead 2 $9.99 (Got it) All L4D maps can be modded on L4D2 servers.

I hope Guild Wars Trilogy's price drop already its $29.99