I just found this excellent presentation made by WiseGEEK that shows us 200 calories from different foods. As you probably know, an adult man should have about 2500 calories a day and a woman about 2000 calories. However, this depends on how a person lives, body type, etc.
The study compares 63 diets initially organized from low to high-calorie density. So you can actually tell how small the sizes are at the end of the list! Statistics show that the average adult needs 2000-2500 calories a day, but this depends on how physically active you are.