Ok I'll argue it then, as prementioned Leon is one of the more fantastic performances of any actors career. Its a powerful performance by a then very young Portman, Throw out the star wars movies which are hard to act in because of the really bad dialogue (legenday actor Alec Guiness always lamented over this when he played Kenobi) and her career is littered with really good to great roles.
Beautiful Girls, Closer, Where the Heart is, Heat and even Garden State while not a oscar worthy type of performance is the reason why fanboys love her. She pulled off the kooky, cute girl next door kind of performance to perfection. And then is able to switch to more pofound movies like Closer.