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 GIRL NEXT DOOR

Heroes star Hayden Panettiere has conquered – and saved! – the world on her hit show Heroes, but in real life she proved to be more than just a spokesmodel and red carpet fixture. The sweet-faced blonde, who's only 18, risked her own life as she took a stand in dangerous Japanese waters to attempt to save a school of dolphins from slaughter.