Caloriecount.about.com does this. I think you have to register, and then you type in the food to see the grade.

maybe this?

http://www.whfoods.com/foodstoc.php

I remember seeing a website awhile back that assigned rankings to a huge variety of foods based on their nutritional composition. I can't remember the site for the life of me, and it is not turning up in my Google searches. Does anyone know the site I am referring to?