Campanula lactiflora (Milky bellflower):
Clusters of blue flowers on tall stems in mid-summer. Ideal for filling out borders and adding height. Fills out quite quickly too. To 1.5m. Hardy.
Very late flowering perennial, tall white flowers with ochre centres in October. Hardy. Up to 1.4m.
Leucanthemum x superbum 'Wirral Supreme':
Tall form of Shasta daisy with white flowers and multiple shorter petals around the golden centre, making an attractive frilly effect. Hardy. Up to 1.5m.
Elegant spikes of golden yellow flowers on black stems above very deeply divided green foliage.