I agree w/ megli's advice re, sun exposure and size of area, as well as existing plants and style. Many flowers do most blooming Spring through Fall w/ the peak in summer. I look for plants that also offer colored foliage and winter berries for year-round interest. Good choices for low water needs and sun are lavendar, salvia, poppy,daylily, euphorbias, teucrium, lantana, buddleia, verbena, coreopsis, mallow, cistus, and sedum. Seeds to plant are rudbeckia, cosmos, shasta daisy, hollyhock, sunflower, and penstemon. Though drought tolerant, plants will need deep watering (more than sprinklers) 2 times a week for 4-6 weeks until established and seedlings reg water until deeply rooted.