If I had to choose one type of plant for the garden, it would probably be perennial geraniums.  They are available in wide range of colours, and different varieiies will flower from early spring right through to autumn.  Solitary bees love them and can often be seen sheltering in the flowers on a rainy day (often the only way I can get a good photo of them).  They will take regular 'hair cuts' and come back to flower just as profusely.  Great planted in a shady place alongside comfrey