A garden looks neat if it has well-defined edges. Low-growing plants are used for softening bed boundaries, as well as for discouraging weeds.
Perennial plants used for edging have to be short, well behaved, and hardworking, i.e., they are best if they flower for long periods or have interesting foliage and texture from spring until fall, as well as minimal problems with disease and insects.
In my garden, they also need to have deer resistance.
Non-flowering lamb's ears meets some of these requirements but needs some intermittent tidying up, though not too much.
Plumbago has nice foliage color in the fall and pretty, blue flowers in both sun and shade, but it's not always as vigorous as I would like.
I really enjoy perennial geraniums and Nepeta, though the catmint, which is Nepeta's common name, only re-blooms if cut back hard after the first flower flush.
Low-growing asters, such as the New England Aster ‘Purple Dome', are beautiful when they bloom in the fall, and the rich color is a bonus.
Verbena ‘Homestead Purple' is another edger with a rich hue that contrasts well with chartreuse foliage plants or flowers of virtually any color.
There are also miniature Shasta daisies such as "Little Miss Muffet', and their pristine white flowers make any border look crisp.