Good choice from Verdun as always. I would add tall Michaelmas daisies for late season colour, especially aster novae-angliae which are more resistant to mildew and phlox paniculata which flower in high summer.
All these are good suggestions. I would try to mix stuff that have different times when they are at their best. It is easy to get a border where everything is in flower at once, and then there is nothing.
Flowering times are easy to look up.
Good luck, planning a border is one of the great pleasures of gardening.
Fennel, especially the purple type and cardoons.
I'd include all of the above but I'd also add some tall dahlias to give a long lasting flower season right up until the first frosts.
Posy, I gave up on fennel, in my last garden it became a nuisance self seeding everywhere and the tap root was a s*d to get out if you left them too late.
How deep is the border ? This would help decide what to plant too ?