Cutleaf coneflower is the perfect 'back row' planting for your irrigated space. The sharply-lobed leaves and towering yellow flowers are a unique backdrop for our other moisture-loving species. Pollinators appreciate the late-season resources, and birds will like the seeds. The seedheads are a go-to in my yard for chickadees and goldfinches. 
 
Some great tall companions include western coneflower, nettle-leaf giant hyssop, blue vervain, and fireweed. Then fill in the front with shorter species, such as black-eyed susan, narrow-leaf echinacea, sneezeweed, and streamside daisy.