There are some perennials that just keep on giving. And giving. The yarrow I grow is a variety called Paprika and here it is almost September with more flowers on it.
The butterfly weed has also bloomed again. All I do is cut back the spent flowers and if I get lucky later on in the summer (meaning now) these flowers decide to give another show.
I couldn't be happier with the purple coneflower. This plant started blooming back in July and I still have some good looking flowers out there. I generally don't cut this plant back as the birds like the dried seed heads from it.
Yes, annuals are the plants that will give you flowers all summer long. But some perennials do pretty well if what you are looking for is long blooming plants.