I'm a fan of Chomsky's system of transformational grammar. 'Government and Binding Theory' is Chomsky's take on transformation grammar. His theory is a mesh of subtheories, one of which, the bit I really like, is x-bar. It's an incredibly elegant way of parsing sentences and transforming between the internal structure and what we actually say. Not that it works exactly, and I'm not sure whether it's made any predictions, but it's on my list of things to learn more about when I finish this physics course.