Winter: Viburnum bodnantense - deeply fragrant flowers on the bare stems, starts flowering about October and carries on till April.
Spring to summer: wallflowers, Viburnum carlesii
Early-mid summer - Matthiola incana, Euphorbia mellifera (a large plant, but almost overpowering honey scent - the name means honey-bearing), sweet peas, pinks. Roses - David Austin in particular breeds for good scent. Sweet briar - the leaves have an apple scent, especially after rain.
Mid-late summer - honeysuckle - google for good fragrance, there are earlier flowering ones and later flowering ones, but not all in either group have a good fragrance. Philadelphus (called mock-orange because the strong perfume is reminiscent of orange blossom), repeat-flowering roses. Sweet alyssum will self seed itself in gravel paths and keep going all summer.
Autumn I find a bit trickier for scent, the Viburnum bodnantense has usually started up again, but that's about it.
Don't forget scented leaves - lavender, catmint, and particularly rosemary. Mints, scented geraniums (come in lemon, chocolate mint, rose, eucalyptus smells) - all the leaf scented things release their scent when brushed against or when a leaf is crushes, so need to be planted along the edges of paths or near where you sit.