Be careful of "whole wheat bread" in supermarkets for instance. By law, they are allowed to proclaim whole wheat on the label if memory serves me correctly if just 8% of the entire batch of the bread is whole wheat.
If reading the ingredient list, it starts with "enriched", put it back. The more whole grain it is, the lower gi it will be. According to the gi scale...
Low GI = 55 or less
Medium GI = 56 - 69
High GI = 70 or more
Remember, glycemic load is much more important in the end than glycemic index. The glycemic index of anything is effected by what is eaten with it. GI is interesting at best anyway, for instance M&M's are lower on the gi scale than canned pinto beans. Which do you think is more healthy, and more productive for your diet?
GI tests aren't based on typical portion sizes of foods. Instead, researchers use a standard measure of 50 grams of carbohydrates of the foods that they are testing. For example, a carrot contains only 4-6 grams of available carbs, so you'd need to eat about 10 carrots to consume 50 grams of carbohydrates -- and it's unlikely that anybody eats that many carrots at one meal. But many people avoid carrots and other nutritious high-GI foods such as beets and squash because of their higher GI values. This is where the glycemic load measurement proves more useful.