The ones to watch: medal hopefuls for London

April 18 marks 100 days until to the London Olympics, a good time to look at some of the athletes who will be thrilling sports fans on the biggest of stages this summer. As London organizers put the finishing touches on the venues, and city officials prepare for an invasion of visitors from around the world, competitors are training for the big moment. From the track to the pool to the hardwood, what follows is a list of athletes to watch (mindful that some still need to qualify).