This perennial cornflower has spiky blue flowers which look like paper cutouts. Their detail can only be seen close up. I cut them back after flowering and often am rewarded with more flowers in autumn.
Centaurea Montana and Fern
Its foliage stays neat throughout the year. I've seen beautiful swathes of this perennial on garden tours, often growing in semi-shade. There is certainly a better effect if it is planted en masse, or given room to spread.
In the Moosey garden I haven't quite got it right yet, so I have to peer into assorted greenery to fully appreciate the flowers of Centaurea montana.