I have worked out IF ratings on a number of my meals, using the IF rating info available at nutritiondata.com - very useful and informative. the nutrient search tool lets you filter for high carb and low or no sugar.. and therefore presumably lower glycemic index, etc.
for example various beans, mushrooms, yams, shellfish... lots of things you wouldn't necessarily think of intuitively as sources of carbohydrate. eg I wouldn't have thought of chicken or beef as carb sources per se, and I wouldn't have guessed that chicken can deliver more grams of carbs per serving than beef, and so on.
all interesting stuff!