Briza media (Lesser quaking grass):
Semi-evergreen grass with beautiful delicate dangling flower heads. Short lived perennial but it will self-seed around. Up to 70cm.
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.