This is the oldest and best so they say.
http://www.weightwatchers.com/index.aspx

The most effective diet is to start eatibng a very well rounded vegatarian diet, you will feel full, healthy and will lose your excess weight.

This could be a good one. Anyone have experience with it?
http://www.southbeachdiet.com

This is a unique diet plan. Not sure it would work for me or if I would ever actually diet :)
http://www.zonediet.com

I dont know how people choose things like this :) So many options all sound similar.
http://www.jennycraig.com