I never saw what sun or shade this area gets. I'm in Central Ky (zone 6) and our summer heat/humidity is a killer. If this is full sun I'd go with a mix of perennials/annuals and one would be the coneflowers (SO many types out there) mentioned above, LOVE it. You could even get dwarf ones for the edge or a profusion zinnia, they are small and bushy and just so pretty. Or gaillardia blooms til the frost kills it here. Perennial phlox is really pretty too and will be nice and full and it also stayed until winter killed it. Also if this is out front of your house, what is the color of your house and trim, then you can make sure you don't put something that clashes. There are quite a few rudbeckias that are beautiful too, I love the Cherry Brandy Rudbeckia and some of the annual ones like Cherokee Sunset, Chim Chimnee, Gloriosa Daisy. I love all flowers though. LOL