I would love to have thalictrums in my garden (the very tall variety as I have a few shorter ones). I also would love to have Marvel of Peru (Mirabilis) purple tubers.
I have rhubarb, English bluebells, autumn fruiting raspberries (red and yellow ones) and lemon balm to swap. I can do cuttings from my rose of attar geranium which is smells absolutely heavenly!
Do check out my In my garden plant listings.