{EDIT 2}ZiLL is right, the deal is back, although you now have to pay $60 instead of $50{EDIT 2}
{EDIT}Apparently, this deal has fallen back into the shadows, it is no longer on Amazon. Congrats to anyone who was able to score it.{EDIT}
...then Amazon has a deal for you.
http://www.amazon.com/2K-Games-BioSh...4903993&sr=1-1
Buy Bioshock for $50, get the Darkness free. You read it right, free.