Often known as sweet Alice or alyssum (ht 20cm), this annual has honey-scented fragrant little bobble flowers and is an old-fashioned favourite. I remember it growing in my grandmother's country garden in the 1960s, where it came up every year on its own on the edges of her paths: it is a determined self-seeder. The most common form is white, but there are also pink and purple varieties. It is a Mediterranean plant and enjoys dryish, sunny positions in the garden. It is often used as an edging plant. It looks attractive growing with other plants of Mediterranean origin that flower in spring, such as lavender, Limonium perezii, tall bearded irises, Marguerite daisies and perennial wallflowers. The flowers are extremely attractive to beneficial insects. Shear off the spent flowers occasionally to promote more blooms.
I have an interesting form called 'Snow Princess', which seems to be a perennial form, growing to a wide mat. It can be cut back by half when the get untidy and will regrow strongly. It has crisp white flowers with a strong scent. There is also a version with pink flowers, called 'Blushing Princess'. The 'Stream' series has similar plants.