Penstemons are really pretty and quite long flowering. Depends on how big a plant you want and what size your planting are is. Geraniums and Hemerocalis are good too.

As Archibald said, it would depend on the types of plants you want and how big is your garden. I have asiatic lilies and daisies that keep on flowering for months in late spring/summer, without my having to do much for them! Both are in a sunny spot..

asters for the autumn too. lupins/delphiniums/ leucanthemums/ aquilegia poppies are all easy to care for.

Small shrubs like azalea or hebe?

If you dont want flowers go for shrubs. I would suggest Hebes. There are so many different kinds, and the ones with varigated leaves I find really nice. A pair of good secateurs is all you need, if you want to be really lazy. There were so many in my front garden when we bought the house, and although I dug out some for my friends I kept some. Just keep them in good shape and the size you like. Maybe I've been lucky, but whatever I do to them for shape, they dont seem to mind. I keep them small (about 1m) and just put some bulbs in between according to the season. Of course when you first buy them make sure the dont grow high to start with. Blue seems to be dominent colour, but from light to purple and also white.