I recommend two plants from the same genus -- a small tree and a shrub -- that are much loved for their rich, bright colors and unfussy culture. Caesalpinia is robust enough to be planted in the asphalt-surrounded medians of Arizona streets. The plants positively bask in the heat, producing flowers in colors hot enough to match summer temperatures.
Mexican bird of paradise (Caesalpinia mexicana) is a small -- 15 feet tall and wide -- thornless tree with pendulous gold flowers throughout much of the warm season. In warmer areas, it is evergreen. This tree looks smart planted in courtyards or near south-facing walls.
Red bird of paradise (Caesalpinia pulcherrima), pictured, produces ruffled red and orange flowers that are as flashy as a flamenco dancer's skirt. A true heat-lover, this big shrub (6 feet tall and wide) will bloom periodically throughout the summer months. In frost-free climates, red bird of paradise is evergreen, but in most Southwest locations it is cut to the ground each winter.