DefenseGrid by Hidden Path Entertainment in Seattle
Age of Booty by Certain Affinity in Austin
and Schizoid by Torpex also of Seattle
DefenseGrid and Age of Booty are also available on PC via Steam and other digital distribution methods, Schizoid is alas Xbox only.
If you like or even kinda like tower defense games, DefenseGrid rocks.
If you even sort liked Settlers of Catan then how could you deny a game inspired by those mechanics but includes cannons and pirate ships! My 7-year old Kyle and I played one Saturday for 10 hours straight.
And Torpex is a visual explosion that is simply a kick ass game to play in coop!