One of my favourite scented plants is Dianthus monspessulanus... (whose name, I discovered recently, has been changed to Dianthus hyssopifolius; yikes, hard to keep up!) It's totally hardy, perennial, and quite unusual, as it has a very pronounced sweet perfume-y fragrance that wafts around beautifully (even in our dry air), as opposed to the usual clove-cinnamon Dianthus scent. I grew it from seed acquired in a trade many years ago. The flowers are a bit tatty and irregular but I forgive all due to the scent! Makes quite a nice medium-height groundcover too (slowly spreading).
