Cephalaria gigantea (Giant scabious):
Very tall wavy stems topped with large lemon yellow scabious-like flowers.Easy to grow. May need staking or support. Hardy. Up to 2m.
Silene fimbriata (Fringed Campion):
Greeny white fringed bell-shaped flowers, loved by bees. Can spread quite vigorously, though will be less so in a dry spot. Hardy. Up to 75cm.