For a quick look at the most common butterflies you're likely to see in your garden, check out the University of Kentucky's How to Make Butterfly Gardens. It will help you identify your favorite butterflies and give you information on the plants they like and how to keep butterflies in your garden.
Favorite or New Plant
With or without butterflies for company, I think purple coneflower (Echinacea purpurea) comes close to being the perfect perennial for the Middle South. A vigorous native that becomes stronger and more heavy-blooming the longer it stays in the garden, this beauty stands up to our sun or you can grow it in part shade. I think the flowers have better staying power grown in part shade and the plants seem to appreciate a break from the sun, too.
Like many other native plants, purple coneflowers become robust when given soil that's been cultivated and amended with plenty of organic matter. Purple coneflower grows best in soil with a near neutral pH, which means the plants usually benefit from an addition of lime every two to three years in our area. Don't be too eager to dig and divide them. Unless you need to increase your supply of plants, let plantings go at least 4 years between major bed renovations.