"Half of the eating is in the seeing," so goes an old saying when it comes to the enjoyment of food. Indeed, food could be made satisfying to the eye (and thereby, the palate) by using garnishes when food is presented. Fortunately, there are a lot of foodstuffs (e.g. veggies and fruits) that could be used in a variety of dishes. Here are a few, and the corresponding suggestions on how to use them.

Chinese parsley and cilantro leaves.
Pluck a few leaves and place on the center of a dish, or just place beside the food on the plate. A more artistic presentation is to place these leaves inside a de-seeded tomato.

Bananas.
You can slice it into rounds, or peel it and scour it with the tines of a fork. A problem with banana (as with apples) is that it oxidizes and changes in color when exposed to air. Prevent this by placing the peeled bananas in acidulated water.

Onions.
Onions as a garnish can be sliced into rounds or into rings. Smaller onions can be used as is, or artfully sliced.

Tomatoes.
Tomatoes can be sliced into rounds or (as is the case with smaller tomatoes) artfully cut to represent a flower etc. Tomatoes are more often than not, not cooked when used as a garnish.

Eggs.
Eggs are first hardcooked before used as a garnish. They can be sliced into rounds, the top part cut-off in a zig-zag pattern and then filled with another foodstuff; or finely chopped and used as a topping.

Cauliflower and broccoli.
These vegetables are actually composed of a lot of small flowers or floweretes. They can be blanched first of used raw before separating the floweretes and used as a garnish. Whether blanched or raw, it's best to dip the cauliflower and broccoli in cold water to make them crisp.

Guavas.
Unripe guavas are ideal for turning into flowers or other carved garnishes. Like bananas and apples though, it also oxidizes easily. As such, dip them in acidulated water to maintain color.

Chili peppers.
Smaller varieties of chili peppers can be used as is - especially if they are colorful. However, they can also be sliced into flowers or into thin strips. They are especially attractive in islands and oriental-inspired dishes.

Native oranges (dalanghita).
Natives oranges can be peeled and the individual sections used as garnish. They can also be thinly-sliced into round (crosswise) and placed on top of a dish; and/or twisted and place around the serving plate or beside the dish.