It all depends what you like and how big your border is... Lupins, delphiniums, phlox, asters, campanulas, primulas, bulbs small and large - the list is just about endless. Scroll down to the bottom of the page click 'b' and then 'borders'

there are 100's if not thousands. many of the plants mentioned on here are border perennials.

'Hardy plants' also includes vast numbers of shrubs, evergreen or otherwise. What you plant depends on the aspect, soil, temperature range, the height and spread of a plant, and whether you like the way it looks or not.