What flower(s) should I choose for my balcony?

I have personally found that Zinnia Pinwheels are perfect for this exact thing. They are super easy to grow and are very forgiving and can take the drought for a few days. They come in variety of colors and don't grow to be too tall (about 12 inches). Just be sure they are the Pinwheel variety, they are they prettiest and shortest of all Zinnias. Good Luck!