Recent research from The University of Tennessee has found that people have a hard time estimating the portion sizes of wedge-shaped foods like pizza, pie and cake. Even when given a special wedge measuring device, the people in the study still had a hard time estimating the size.
In light of this, it would seem wise to stick to non-wedge shaped foods or ask that your pizza be cut into squares instead of wedges. Make cupcakes and mini pastries instead of cakes and pies. I can't believe I am even saying this but cut cheeses and quiches into squares. I know it seems odd but it's still the same food, no matter how it's cut. This way you'll be a lot more apt to be able to judge the portion size of what you're eating.