A lot of these summer flowers leave their skeletons behind in the fall, but they can be interesting even as the snow falls on them. We have several Black-eyed Susans and condflowers that come up each year which give us lots of flowers through the heat, but are interesting after they've dried, too.
We planted some Little Bluestem a couple years ago. This time of year it's only about 6" tall, but it will get up to 18" in the Fall and turns a deep orangish red. If you have a bigger area, Big Bluestem will grow to 4-6', especially if it's getting some water!
One smaller wildflower that comes in lots of varieties is the Buckwheat family. We have several on Green Mountain. The one that's blooming now is James Buckwheat (Eriogonum jamesii). It's gold flowers are on an umbel, so they have a lot of color in a small area. The other I'd recommend for a yard is Sulfurflower (Eriogonum umbellatum). It blooms earlier, but both of these flowers keep their shape after they've gone to seed, and the plant turns a rust color that's still attractive.