As Apple's iPhone and iPad get more and more games, it's only natural that more and more co-op titles are in the mix.  One such game, adding in a co-op mode via expansion, is Tilt to Live.  As you can tell from the screenshot above, Tilt to Live has a definite Geometry Wars feel to it.  And believe me when I say, that is a very good thing.  The new expansion, appropriately titled "Viva la Co-Op", allows for two players to connect via local wi-fi or Bluetooth.  One player controls the motion of the ship, while the other is in charge of the turret itself.  Tilt to Live will set you back $2.99, and the expansion clocks in at an affordable 99 cents.  Check out the trailer below.