Some tall, narrow perennials that require no staking or pruning to maintain their shape include:

Palmer's penstemon (penstemon palmeri), 'Autumn Minaret' daylily (Hemerocallis 'Autumn Minaret'), Ava's hummingbird mint (Agastache x'Ava'), 'Herbstonne' coneflower (Rubeckia 'Herbstonne'), Joe-pye weed (Eupatorium fistulosum), Maximilian's sunflower (Helianthus maximiliani), Prairie dock (Silphium terebinthinaceum), and West Texas grass sage (Salvia reptans). All require full sun with the exception of the 'Herbstonne' coneflower which can take some shade.