Zanthoxylum: - Small trees or large shrubs - as you wish!
Zanthoxylum piperitum - the Japanese Pepper Shrub - is evergreen, hardy and has large glossy leaves as foil to yellow green flowers, followed by red fruits.
Zanthoxyllum simulans is deciduous and probably best if allowed to grow as small tree - rather than a large shrub.
Zauschneria: - Near hardy low growing sub-shrub is a blaze of scarlet flowers in midsummer through to autumn. Needs a dry sunny position. Dry stone wall, rockery or container, are suitable places.
Zelkovia - Sometimes large shrub but normally classed as a tree. Normally spreading often as a multi-stemmed type
Zenobia pulverulenta: - An ericaceous - fully hardy but deciduous spreading shrub, is used mainly for landscape cover work in acid soil conditions - or woodland.