Hi Nick,
Extending the Thymus theme, most of the Lamiaceae have scented foliage. There are some genera with very dwarf forms such as Teucrium, Salvia, Origanum, Scutellaria etc. Most of them need a lot of sun and very good drainage.
On the bulbous front there are lots of dwarf Allium, most of which have scented foliage.
Not really an alpine as such but chamomile is dwarf. I suppose it could be grown in a trough - maybe a good one to underplant with bulbs?
Most Geranium and Erodium also have scented foliage (not as good as Pelargonium admittedly). Though most are too big for a trough, some are dwarf especially the Erodiums.