I would imagine you could go for most of the shorter herbaceous perennials (Phlox, Helenium, Monarda, Knifophia, Agapanthus, Agastache etc) providing they're kept watered and fed.

Verbena bonariensis grows a bit taller and makes a lovely foil for other plants. I always grow some in tubs among other tubsof shorter perennials.

Cannot disagree with the above apart form add in hosta.