Ceanothus

A dense bush of a California lilac, it has masses of blue flowers in spring and early summer above the dark green foliage. Like its species parent, it's extremely reliable. A good alternative is 'Puget Blue', which is a magnificent dark blue. The impressus kind aren't totally hardy, but given a sunny, sheltered position, they should thrive without any problems. They can be trained against a wall where they've been known to reach up to 4.5m. Avoid cold, exposed sites, and give a light prune after flowering.