I get the impression that Spiraea is one of those groups, like Hypericum, that most keen gardeners tend to scoot past, and generally speaking I'd do likewise, but I've come to learn that almost every group has something choice to offer and it can be fun locating it.
Spiraea thunbergii is one such gem - hardly an obscurity (it has an AGM after all) but I hardly ever see it in gardens or nurseries. It is an exquisite shrub combining sprays of pure white flowers with the lightest and freshest of pale green leaves, all in a loose billowing (but not overly large) arching shrub up to about 4ft tall and across. Mine flowers surprisingly early in the year (March) and goes on into May. After that the foliage and form make a very pleasant contrast to darker heavier plants, and are never even slightly ugly.
Can be pruned quite hard after flowering if neccessary and I imagine it would make a good informal hedge.
Very easy to please on any soil in sun. Absolutely spiffing in every way.
1L pots ~ £7