check out: corydalis elata (blue/lavender flowers, compact). I just got one. See site below.
geraniums: quite a large selection to choose from (various blooming times and shapes--most have fragrant leaves)
Phlox divaricata --light blue flowers, compact--fragrance is simply divine, but would not bloom for more than 4 weeks, I think-mine started blooming around May 25 and is still going strong.
Also how about a nepeta? I have a 'souvenir d'André Chaudron' that does very well in part shade and which blooms all summer.
Many tiarellas bloom a long time, but .. no fragrance

Just some suggestions that came to me right away.
Good luck,
Anne-Marie (now living in Maine)

Here is a link that might be useful: corydalis elata

Thanks, Ann-Marie---the corydalis looks lovely. Where did you get yours? I'm heading for Longfellows tomorrow. I hope they have one!

Hi, Mainerose
Got one last week at Fernwood Nursery just outside Belfast (such a wonderful place!!), but I am sure Longfellows would have it (unless sold out)... and it is hardy to zone 4 (I realized you were in a colder area after I posted my message). Thought it might fit your space well. The fragrance is a definite plus, too!!
Good luck, Anne-Marie