Best of 2007

21 & Under: Hottest Breakout Stars

Zac! Rihanna! Shia! Lauren! These kids aren't only the most popular, they're also the most likely to get bigger in '08. By Aaron Parsley

THE BOMBSHELL

No one was caught without an "'ella, 'ella, 'ella" this summer thanks to the season's catchiest song, Rihanna's "Umbrella." And while artists as diverse as Mandy Moore and My Chemical Romance covered the sexy hit, the ubiquitous Barbadian beauty and VMA winner, 19, became a Cover Girl herself, modeling for the makeup line.