Katherine Heigl

Though her filmography is longer than you'd expect for someone her age (she's been appearing in films since the age of 12), Katherine Heigl's role in Roswell introduced her to Generation Y.

This generation matured since the end of Roswell in 2000 and developed more mature tastes in TV shows, and luckily for them, so did Katherine Heigl. She reappeared for her grown-up fans in the Golden Globe-winning hospital drama Grey's Anatomy and fun flicks like Knocked Up (2007) and 27 Dresses (2008).