Daphne caucasica I love this plant so deeply it is almost obscene, and for one simple reason: Fragrance. It is wonderful, and the kind of carrying fragrance that travels far. Customers smell while shopping for something else and have to take a moment to track down, and then have to have one. Better yet, flowering is pretty much continuous. Walk by the plants basically any day from May to October or even early November, and they'll have flowers on them, pumping out that exquisite perfume. Forms an upright shrub probably topping out around 3 feet. I consider it absolutely essential to happiness. Zone 5, at least.

Closely related to collina, (Halda lumped collina into sericea but I doubt if anyone will take it seriously I agree with robin that the two are distinct and the Turkish forms are quite different from the Cretan ones) the heads of sweetly scented lilac flowers, are produced in spring and it generally reblooms later in the summer, in the garden it will make neat rounded mounds 2-3' in height.