However I can tell you from personal experience that the good old Buddleia isn't called the 'butterfly bush' for nothing. (It's also very popular with bees!)
I can second that. I have four Buddleia bushes in the garden, along with the spikey one that I haven't identified (which inspired my screen name). All of which bring huge volumes of bees, butterflies and hoverflies to the garden.
Apart from being very fragrant, my Buddleias have grown some very rude looking blooms. Meat & two veg-shaped. Source of great amusement.
There are several varities of Bee Balm (Monarda) from smaller ones about 8 inches tall to standards that are nearly 4 feet tall and in many differing colors. All are very fragrant, including the stems and leaves and very attrative to bees and butterflies... easy to grow and hardy as well...
We have a scented climbing rose up the back of our house, and during the summer when it's flowering, the sound of the bees in it can be really loud, dozens of them come to it.
Strong scents attract flying insects, so go for plants with long flowering times and a scent.
If you have a large garden plant flowering shrubs, especially a winter honesuckle...mine's covered in flowers at the moment, it smells heavenly and the bees are loving it on a mild day.
Hebes, cotoneasters, lavenders, sedums and marigolds are always covered in insects in my garden.
thank you to all i already have at least 6 buddleia and a couple of honeysuckle along with 3 clematis but am after some smaller flowers like snapdragon & single dahlia
Achillea Gold plate or similar.
Erigeron
Echinacea
Solidago
Portuguese laurel but it will need to get big to flower really well
Lavender
Single roses
any single daisies Helianthus, single chrysanths and 'michaelmas daisies
Candy tuft
Ajuga
Echiums
Pot marigolds
Sedum Spectabile
Passion flowers
Jasmine
single type gladiolus
Viburnum
cotoneaster
ivy in the shrub form
loads more
Extensive list there rowanwitch , but I'd add verbena bonariensis which is tall pale lilac and airy,see through and I've had the relatively rare hummingbird hawk moth on mine in the past .... Spectacular! The seed is pretty easy to germinate and grow and,once established,will readily self seed. Bees particularly like the pale blue of borage ... Again easy to sow,and grow.