Web 2.0 dieting and nutrition site: Sparkpeople.com
I have been extremely impressed with http://sparkpeople.com. This is a web 2.0 site that allows you to count calories, track cardio and other goals, interact with others via spark blogs, spark email, and spark teams. It is interactive all the way to the bone.
As the New Year rolls around, I think many are looking to implement a diet. I have been using this site for a few days now and I think it is certainly the coolest tool I've ever seen for nutrition and fitness.