1.  Grapefruits
Grapefruit known as the best as a diet food.

2.  Hot peppers, chili pepper
It give a quick boost to the metabolism.  They also prove that healthy food is not necessarily bland.

3.  Apples
Try an apple in the morning during breakfast, it will make you feel more full so you can eat less.

4.  Avocadoes
Avocadoes contain more than  25 of the essential nutrients: B vitamins, potassium, vitamin E, and lutein,  make you keep healthy and no need eat more.
5.  Broccoli

Its high in calcium, iron, magnesium, vitamin A, and vitamin C.  It’s filling without being high in calories, it is also an anticancer food.

6.  Blueberries
Blueberries are full of powerful antioxidants.  They fight against disease, give you energy, and their sweet taste makes a great snack.

7.  Almonds
Have a handful of almonds in the morning during breakfast to give you energy for the rest of the day.  They are also great to replace any unhealthy snack foods which are standing in the way of your weight loss goals.

8. Soybeans

Most health food, contain lecithin, this chemical will shield your cells from accumulating fat.

10. Fish
Low in fat, as high in protein as red meat.

Some information of diet foods on Wikipedia.