There is a specific site called EDiets that works as you describe. You sign up and pay so much per month, and you tell it your goals and preferences, such as whether you want to use mostly convenience foods or cook your own meals. Then it gives you a menu each week, complete with recipes if you have chosen to make any meals on your own.
I have a friend who used it and liked it, but it can be expensive at first because it gives you a lot of variety. It might call for Raisin Bran for breakfast one day in a week, but then you will have 6 other things for breakfast that week instead of Raisin Bran.