What else do you have planted nearby, how much room is there, do you want something vertical, as with @fidgetbones' suggestion, or something lower growing? Colour preferences? Flowering now or in summer?Almost any hardy geranium would do. Other verticals like Heleniums which have strong, orangey colours will flower at the same sort of time, or Crocosmia if you like those colours. Schizostylis, now called Hesperantha, comes in a white variety, and flowers at this time of year.
I'll second the blue asters. I have had Aster frikartii 'Monch' in flower for ages and it is still going strong. I have it near my front gate so love to see it every time I go in or out and I can also see it from my bedroom window.