just something that stays looking nice throughout the season. I'm toying with the idea of some variety of sunflower along the fence line...but what to do, otherwise?
I have a few ideas for you. Try Heliopsis helianthoides. It's a native US plant that resembles native sunflowers. Gets about 4-5 ft tall, and looks best when you grow many of them close to each other.
You may also consider Penstemon. It doesn't flower long, but it looks great even after it's done flowering.
Gaillardia is a great choice. If you deadhead it, it'll flower from late spring until first frost. It's also a member of the sunflower family. Here I planted 4 plants about 8 inches apart.
and the plant that I recommend to everyone is Orange Milkweed. It's my favorite plant. Looks great, is necessary for Monarch caterpillars, and around here it blooms from early June to late August, sometimes into September. Looks best when you plant a few within inches of eachother.