Harriett, I lived in a place 30 year ago that had heavy clay soil. Like you, I had pretty good luck with iris I tried to amend it and grew some orange daylilies, purple coneflowrs, and some sedum. I hated that clay soil, but back then I didn't have the proper resources to amend it. Good luck. I'd love to hear what works.

Is your clay always damp? The reason I ask is that there are some plants that don't mind damp clay so much, but they struggle in the years when it is incredibly dry. In my garden, where the clay has been amended for years and years now and spends as much time bone dry as it does wet, I grow pretty much the same things you have and also have echinacea, rudbeckia, autumn sage, mealy sage, various daylilies, Texas hibiscus, cannas, red hot poker, veronica, oriental lilies, spiderwort and crinum lilies. Oh, and for spring color very early in the season, there's daffodils, ornamental alliums, Dutch iris, and Dutch hyacinth. Even better than perennials, I have a lot of reseeding annuals that reseed so well that they tend to spread beyond their assigned spot in the garden. They reseed for me so well in the same spots that my friends insist they are perennials and not reseeding annuals, but that's not true---they reseed in the same area but aren't necessarily coming back from the roots. The plants that reseed for me in clay (and some of them are in only barely-improved clay) are: corn poppies, Oriental poppies, larkspur, pink evening primrose, moss rose,Texas bluebonnets, snapdragons, verbena bonariensis, Laura Bush petunias (heat-lovers bred from native petunias), gomphrena, zinnias, hollyhocks (probably actually biennials but they reseed so well that I've got new ones in bloom every year) and Malva sylvestris 'Zebrina' and 'Mystic Merlin'. I almost forgot to mention four o'clocks, They get significantly bigger in our sandy soil areas, but also grow quite well in clay. In our clay pastures we have tons of wildflowers that reseed themselves, so don't overlook those as a possibility too. Every few years (usually after a bad drought year when the wildflowers didn't live long enough to make seeds) I overseed the pastures with either the TX-OK Wildflower Mix from Wildseed Farms or the Poppy Mix or their Firecracker-1-2-3 mix. In the horribly hot and dry drought year of 2011, I found that some plants that were happy in damp clay most years couldn't survive in dry clay baked as hard as concrete, but we don't have many years like 2011.

For the most part, I just avoid anything that needs good drainage. As long as the perennials don't strictly require good drainage, they don't seem as unhappy in clay as you'd think they might be.