wisegeek writes:

Some foods have significantly more Calories than others but what does the difference actually look like. Each of the photographs below represents 200 Calories of the particular type of food; the images are sorted from low to high calorie density. When you consider that an entire plate of broccoli contains the same number of Calories as a small spoonful of peanut butter, you might think twice the next time you decide what to eat. According to the U.S. Department of Agriculture, the average adult needs to consume about 2000 - 2500 Calories to maintain their weight. In other words, you have a fixed amount of Calories to "spend" each day; based on the following pictures, which would you eat?

Today I learned that you can eat a lot of mini peppers or broccoli for 200 calories:

And apples and melons, too.

FAQ:

Why 200 Calories? We could have chosen any amount of Calories for this project, but we wanted something that gave tangible volumes for the entire range of items. We felt that 100 Calories of butter or oil would have yielded diminutive portion sizes; on the other hand 500 Calories of celery would have been virtually incomprehensible.

How did you choose which foods to include in the project? Many of the items we chose just happend to be in the wiseGEEK pantry; we chose the others because we wanted to display foods in a wide variety of categories. We stayed away from prepared foods such as funnel cake andspanakopita because their Caloric content is closely tied to the particular recipe used; we also avoided some more obscure foods such asmangosteen and jackfruit. 

The sorting can be misleading because items with liquid tend to appear less Calorie dense; thats why you will find coke amongst the vegetables and cooked pasta significantly higher than uncooked pasta. 

All pictures were taken with the same camera (Nikon D70 digital camera) and with the same setup; in other words, the portion sizes displayed are all relative to each other. 

The plate is 10.25" (26cm) in diameter and the bowl is 6.25" (16cm) 

This article deals with Calories only. Don't forget that there are other considerations when choosing which foods to eat, such as nutritive value and diversity of your food choices. 

The capital "C" in "Calories" throughout this article denotes dietary as opposed to physics calories.

Seriously this is worth clicking through:

http://www.wisegeek.com/what-does-200-calories-look-like.htm

And now it's an app:

http://pandawhale.com/post/53645/what-200-calories-of-every-food-looks-like