Purple Coneflower (Echinacea purpurea) - Perennial with tall stems & long-lasting, lavender flowers that bloom April - September. 
 
Growth: Can grow 2 - 4 feet tall.
Light: Full sun
Soil: Likes well-draining neutral or slightly acidic soil.
Hardiness: Tolerant of heat, drought, humidity, & poor soil.
Maintenance: Water deeply & infrequently, about 1 inch per week. Divide clumps when they become overcrowded (about every 4 years.)
Benefits: Attracts butterflies, hummingbirds, & other pollinators.