I hear a lot of clients complain that they eat breakfast and find themselves still hungry soon after.

usually its because there wasn't enough breakfast, personally i aim to have a little carb, a little protein and a little fat with each meal including breakfast. this made a huge difference in my hunger, because i was balancing things out with the macro-nutrients.

Nancy clark in her book recommends 500 calorie breakfasts. i think this might depend on the person.