19. Serena Williams
Occupation: Professional tennis player
Biggest accomplishment this year: Upcoming participation in the 2013 French Open and the 2013 Wimbledon Championships
As of right now, Serena Williams is the No. 1 ranked female tennis player in singles, and shows no signs of losing the energy that carried her through last season, when she was named WTA Player of the Year for the fourth time in her career. She's currently participating in the French Open, where she's set to face against Caroline Garcia.