5. Natalie Portman, 'Black Swan'
Undertaking a year of ballet training to prepare for her Black Swan role, Natalie Portman delivers a worst-case/best-case scenario of an artist's need to push herself beyond her breaking point to make something that lasts. Both the beauty and the madness inherent in pursuing perfection is written all over the actress's face, resulting in the sort of go-for-broke portrayal that leaves you in thrall, even if you remain fearful that the woman giving the performance might break in the process. But Portman never wavered: In a career that began with the icy confidence witnessed in The Professional, Black Swan was the culmination of the delicate/steely juxtaposition that is often at the heart of the characters she plays. This psychological thriller often risks flying right off the rails, but Portman gives the movie its empathetic grounding.