Celebrating 15 years of Hitman (I really feel old now) Square Enix is offering Hitman 2: Silent Assassin for free.
As far as Hitman is concerned I think I can safely say that the series only became incredible with Blood Money but even so Hitman 2 is a classic and worth your time if you enjoy that type of game, if for no other reason than to experience a bit of history.
NOTE: In order to claim your copy you will need a valid US address.
The procedure is pretty simple:
-Make a Square Enix account
-Add Hitman 2 to your cart
-Add the "FreeSilentAssassin" code
-Complete the purchase
-Go to you account -> my orders -> your hitman purchase -> grab your Steam key from there
While you're there you should also check out the various sales they have going on, you might find something that interests you.