The Spanish introduced metal (the natives were still using obsidian for weapons), gunpowder weapons, horses, and most importantly, a multitude of diseases that made the Black Death look like child's play.
The natives (specifically around present day Mexico) introduced chocolate in the form of cacao beans, sugar (I think), cotton, corn, and a variety of other crops. Really, the Spanish were into the New World because of how much gold they had, not the new types of food.