The Center for Nutrition Policy and Promotion (an agency of the USDA) has a website, the interactive healthy eating index, that allows users to analyze their dietary consumption for a number of factors. After users enter the food they ate on a given day, the site analyzes their diets according to nutrient intake, an overall "healthy eating index," and the food pyramid. It can even track users' consumptions across multiple days.
When I get to digestion in my class, I give students the option of analyzing their diet using the CNPP site as one of their semester projects. The students track their consumption for two days, enter the information onto the website, and then write a report analyzing the healthfulness of their diet. They also have to pick one nutrient that they consumed unhealthfully deficient or excessive levels of, and then use the program to figure out how to change their diet to correct the problem. I haven't had a single student yet who was unable to find a problem nutrient :)
Student reaction to the project is typically ecstatic; many had no idea resources like this were available, and almost all of the papers include comments that they hope to be eating better because of this project.