According to Lisa R. Young, Ph. D., the author of "The Portion Teller Plan", 3 oz. of meat, poultry or fish is about the size of a deck of cards; 2 tbsp salad dressing is equivalent to 1 shot glass; 1 tsp butter or margarine is the size of a postage stamp; 1 oz. cheese is equal to 4 dice; 1/2 cup rice or pasta is half a baseball; and 1/4 cup nuts is a golf ball.
The next time you're eating out, just remember these visual cues to avoid overeating. :)