exercisefriends.com Find clubs or workout partners in all arenas, from dodgeball to kayaking and more.
yoplayas.com Find workout buddies in your area at your same level of fitness.
meetmarketadventures.com Singles adventure outings in select cities in the U.S. and Canada.
nikeplus.nike.com Use a Nike+iPod device and join one of the virtual running and walking challenges online. It won't get you a real-time workout buddy, but you can virtually compete with other people who have your same fitness goal.