If you like to display cut flowers from your garden, often missing from arrangements are foliage and filler plants. Floret Flowers, a flower farm and seed company in Skagit Valley, WA, has written an excellent article on this subject (link below).
Here are some of the of the plants listed that work well as fillers:
Bells of Ireland, Bupleurum, Euphorbia, Honeywort, Mint, Queen Anne’s Lace, Sweet Pea vines, Basil (purple particularly), Dusty Miller, Dill, Bee Balm (Mondarda), Love-in-a-Puff vine, Raspberry Greens, Red Leaf Hibiscus, Scented Geranium, Shiso, Flowering Tobacco, Ninebark, Apple of Peru, and Oregano.
There are some beautiful photos in the article as well as good descriptions and how to grow instructions.