Christina Aguilera & Lil' Kim, Mya and P!nk

A leader in the parade of Mickey Mouse Club veterans who stormed pop music at the turn of the millennium, Christina Aguilera was the sexy, brassy diva of the bunch -- the Rolling Stones to Britney Spears' Beatles, as it were. Initially, it was difficult to see Christina outside of the prism of Britney, whose 1999 success launched the new millennium's teen pop boom, but Christina's big hits of 1999 -- "Genie in a Bottle," "What a Girl Wants," "Come on Over" -- more than held their own with "...Baby One More Time," while revealing a vocalist with considerably more power and rang...