CHUNG SUNG-JUN—GETTY IMAGES

Heather O'Reilly, 23, Soccer

Heather O'Reilly, 23, wears Mia Hamm's No. 9 jersey. O'Reilly was the youngest player on the team at the 2004 Summer Games in Athens, Greece. There, she scored the winning goal in the semifinals for the gold-winning team. She followed her Olympic run with a brilliant career at the University of North Carolina, where she scored 59 goals and won two national titles. O'Reilly is switching positions for the Olympics, from forward to midfield, to take advantage of her size and speed. She'll be under even more pressure now that her teammate, Abby Wambach, has been hurt. The U.S. is defending gold after a third place finish at the 2007 World Cup.

--By Sean Gregory