If structure is important to you, you might want to look into the plan I've been following, Jenny Craig. It's well-balanced, sane, supports your metabolism, and can provide you with a menu all planned out if you like. It's also very convenient because of the meals you purchase from them. They help teach you about portion control while relieving you of some of the decision-making early in the program. Then, as you get closer to goal, you start branching out more and more on your own. I also find the individual consultations invaluable.
Just remember -- "following a diet" isn't enough. You have to use the tools of whatever plan you use to makeover your lifestyle. While being on JC, buying the entrees, and following the planned menus have helped me lose weight, doing a lot of mental work on the reasons why I overeat and concentrating on developing good life-long habits are what have kept me going and will keep me at healthy weight long after I reach my goal. It's easy to burn out on "diets" and rebel -- developing an attitude that you are going to eat differently from now on is the key to true success.