Plant color for the heat. I like to use plants with colorful foliage, like coleus in shade. Persian shield is another great one for those shady areas.
Raise the mower blade, if you haven't done so already. By mowing too short, you're inviting root stress and weed problems. Higher grass keeps the roots cooler and won't dry things out so fast. Remember that the best watering technique is to water deeply but not too often, since that can cause fungal problems. But start by raising the mower blade.