Amazon is BioShock Infinite. Downloadable PC versions of the game are $25 off ($35), whereas boxed copies of the PC, Xbox 360 and PS3 versions are $20 off ($40) for today only.
Meanwhile, $35 Steam codes through Groupon for the game appear to still be available until the end of the day. What we're trying to say is, today might be a good day to buy a new game.
[Thanks to everyone who sent this in!]