Credit to my friend who just pointed this out to me as he was trying to find people who hadn''t already purchased Left 4 Dead (he has been unsuccessful).
Apparently Steam just put up a deal to get 4 copies of Left 4 Dead for $37.50 each with instant access when the game launches, of course. Works best with people you know will pay you back You''ll need the Steam account ID of your fellow Survivors to send the copies.
Just enter Steam and click on the $44.99 Left 4 Dead offer and you''ll see it listed as the second item on that page; or, click here.