The heat of summer can be stifling here in the Dallas area. It is also a difficult time of year to find plants that can perform well without melting.
A couple that I've found that seems to take the heat well are the Texas bird of paradise or Caesalpinia gilliesii and dragon wing begonia a begonia hybrid.
The Caesalpinia gilliesii requires full sun. It starts blooming in July and through the summer with yellow petals accented by longer protruding bright red stamens. The plant's foliage is fine textured and contrasts well with bolder foliage plants like dark leaf cannas or red leaf banana. It can be cold tender in north Texas dying to the ground only to return in the spring.
The dragon wing begonia is an excellent plant for shady areas. Plant in well prepared beds or in pots. The foliage can be easily broken so keep away from anything that might brush up against it. This is an annual and will freeze with the first frost of the season.