I have L4D for PC, and am willing to sell my Steam account to anyone who is interested. It has L4D, Day of Defeat Source, all the Half Life games and episodes, Team Fortress 2, Portal, Counterstrike Source, etc.
[quote name='jonac13']The game is $37 on Steam.[/QUOTE]
This is the best deal you can get for now. Being a steam game it is linked to your account, so you can't resell it. You don't even really need the DVD after installing.