Just catching up on the board and discovered this lovely offshoot from my Bauhinia question. Some lovely suggestions there from everyone. Scent has always been a huge component, for me, of what makes gardens (and being outdoors in general) attractive.
There are the refined perfumes, of course: Jasmines various (I love them all), Hedychium coronarium (!!!), tuberose, Gardenia, Trachelospermum. I would put Pinks here too; that clovey richness sends me into transports of delight...
Roses deserve a category all of their own, or perhaps separate categories for the different kinds: old English, Hybrid Teas, ramblers, rugosas... and their foliages also have often interesting and pungent scents. A couple of my favourites off the top of my head are Sweet Juliette (almost citrussy) and Mmme Isaac Pereire, but I could go on for AGES. For now, I will just to add the fragrance of a single white rambler rose that grew in one of my gardens, which I suspect was Rosa filipes "Kiftsgate".
The pungents that hang in the air, often at some distance from the source plant, I also love - Eleagnus, Daphne, honeysuckle, Lily of the Valley, Pittosporum tobira. On the subject of mock oranges, is it just my impression or does the dwarf Philadelphus "Manteau D'Hermine" have a much sweeter, finer fragrance than the slightly club-hammer hit of the majority of them?
Soft scents, those that you have to get your nose in to appreciate: Iris, jonquils, Phlox, violets, lilac.
Nighttime scents: Cestrum nocturnum, Brugmansia, stocks.
The mediterranean plant spectrum of course contains a lot more scented foliage - oily saps and all that - some of my favourites are Calaminta nepeta and a particularly good Origanum marjorana variety I had the luck to find last year - like perfume. Aloysia triphylla, Melissa officinalis, Thymus citriodorus and Cymbopogon citratum give very different expressions of the lemon scent that comes presumably from similar compounds. Going into scented woods, I saw (and smelled) the cinnamon tree for myself for the first time last year in Majorca; a Cinnamomum species. Delicious! And what a treat when I discovered that the leaves of citrus fruit trees smell like their fruit (lemon, lime, grapefruit…)
But I have to conclude the list with an appreciation of the compound scent of the Algarve air; it changes through the year and according to where exactly you are in the landscape, but the foundation ingredients are Cistus ladanifer gum, oleander blossom, toasting pine sap and fig: unfurling fig leaves, later ripening figs. Truly, heaven is a place on Earth.