You've made the resolution to get fit, but now you need someone to hold you accountable. Let the denizens of Social Workout help. Not only is the upstart blog a good source of fitness news and profiles, there's a message board with preset programs (and fellow participants) to help you shape up. Sign in with your Facebook profile, and participate with your friends, or post messages touting your progress on your wall. There's even prizes for completing the programs. (Social Workout, free)