Fitocracy is a fitness gamification social site for logging and tracking workouts. It has an RPG like system with quests and leveling up. It makes it very easy to make public commitments to a workout plan and provide each other with motivation and advice.
I shouldn't really have to go over why you need to be working out if you plan on living until the singularity :)
that's the url fitocracy supplies for group invites.
alternately you can use the add code on the fitocracy landing page: Y3JQP