Julia Roberts is the top female box-office star in the world,the highest grossing actress of the past decade,according to a poll by Warner Bros.Her films have raked in half a billion dollars.The auburn-haired superstar recently cracked the all-male $20-million-per-picture club whose chartr members include Tom Cruise,Mel Gibson,Jim Carrey and Tom Hanks. Last summer,Roberts starred in not one but two romantic comedies that seemed as close as possible to being sure-fire hits.Notting Hill,abouta shy London bookshop owner who falls in love with an American movie star,paired her with Hugh Grant and the creative team that made Four Weddings and a Funeral an international hit.Runaway Bride,a vaguely autobiographical tale about a woman who repeatedly dumps her groom at the alter,re-teamed Roberts with her Pretty Woman collaborators,Richard Gere and director Garry Marshll. In the upcoming Erin Brockovich,which nabbed her the record breaking $20 million payday,the actress gets to flex her dramatic muscles in a real life story about a legal secretary who helps win a giant class-action lawsuit against a major industrial polluter.