Barbecue.
Pizza and burgers may be more commonly eaten here, but they're really adaptations of food from Europe. Brisket, ribs, or pulled pork, slow cooked in a pit smoker and smothered in barbecue sauce, are more American in origin, and extraordinarily delicious.
There are lots of regional variations too. Mostly a result of what resources were available (ie, it's smoked with whatever wood is readily available in that region), but now they are a strong point of regional pride, and the topic of endless "which region has the best BBQ" debates. (I'm a fan of Memphis style, myself, but it's all good.)