What a good idea, Umbrian.
I thought I would produce a list of my top 10 plants but others kept creeping in, so I ended up with a much longer list of plants that have done well under our conditions. I wouldn't be without any of them. A lot are good old stalwarts and not terribly exciting. The vast majority are drought-tolerant (d-t) unless otherwise stated.
Trees:
Pinus pinea - stands up exceptionally well to drought/wind, but is slow-growing
Olea europaea - a must for a Mediterranean garden
Albizia julibrissin - smallish tree, impressive in flower
Punica granatum - compact with lovely flowers and fruit
Juniperus oxycedrus - attractive needles, tough but prickly
Shrubs (large):
Nerium oleander - with a little summer watering it flowers from May to October; what more could one ask for?
Spartium junceum
Lygos (Retama) monosperma - very d-t, white flowers
Medicago arborea - long flowering season, self-seeds, but summer-deciduous
Arbutus species
Laurus nobilis
Phillyrea angustifolia - dense evergreen
Rhamnus alaternus - good for evergreen hedges
Shrubs (small):
Scabiosa cretica - pretty blue flowers followed by white seed-heads
Myrtus communis
Salvia leucantha
Teucrium fruticans
Rosmarinus officinalis
Westringia fruticosa - similar to rosemary but with a better shape
Limoniastrum monopetalum - very d-t with tough grey leaves and pink flowers, but not hugely attractive overall
Hibiscus rosa-sinensis - not d-t, but gorgeous non-the-less
Pelargonium x hortorum - good old geraniums; if in shade they cope without water
Felicia amelloides
Cneorum tricoccon - interesting little shrub
Perovskia atriplicifolia
Phlomis fruticosa
Cistus creticus/parviflorus
Euphorbia characias
Bulbs:
Cyclamen hederifolium - trouble-free, looks lovely under trees
Tulbaghia violacea - a long-flowering toughie
Groundcover:
Convolvulus sabatius - forms a dense mat with pretty blue morning glory type flowers
Succulents:
Aeonium arboreum
Climbers:
Bougainvillea spectabilis
Tecomaria capensis - easy, long flowering season