While Rihanna's biggest smashes inhabit 21st-century pop's hooky, hip-shaking ideal, her catalogue is full of left turns into unexpected territories. The thundering, mournful “American Oxygen” casts a gimlet eye on the American dream; the Future collaboration “Selfish” allows her to show off her silvery, sensuous upper register; and her reverent cover of Bob Marley's “Redemption Song” is a striking tribute to her Caribbean heritage.