Obviously, foods with a lot of sugar in them tend to be very glycemic. But people are sometimes surprised to hear that the starches in foods such as potatoes, bread, and grain products are made up of long strings of glucose, so these foods can be as or more glycemic than sugary foods. Also, the more processed a food is, the more glycemic it will be. So, for example, instant oatmeal in the packets is more glycemic than quick-cooking oats, which in turn are more glycemic than steel-cut oats.
For diabetics, glycemic control is a primary goal.
See the Glycemic Index Food Lists to learn more about the glycemic index of various foods.