Hey, I was just reading up in my text on zone 4 and you should be happy, check this out...
"No zone grows better perennials and bulbs; people who like woodland plants and rock plants love zone 4."
woodland plants = shade plants so w00h00!!
Just checking out some of the possibilities cross-reffed with my sunset guide...
Acanthus Mollis - Bear's Breech : Mollis isn't listed for zone 4, but its cousins Acanthus balcanicus and Acanthus spinosa are. I happen to like this plant, but it's a little weird looking so I'm sure it's a matter of personal taste. Does very well in shade. It needs water though, so if you want low-maintenance then maybe it's not the plant for you.
Hostas are another plant I love and would do well in your climate and in shade, but again, they will need watering. Have you considered setting up an automatic irrigation system?
Hydrangeas, again need water but should do well in your climate.
Sword fern is the same. Great looking, does well in shade, but under a cedar would require additional watering, especially in the summer.
I think I may have mentioned Impatiens before. I don't think they could be grown as perennials in your climate, but Gopher will know more.
Mahonia nervosa is a groundcover that might be something worth looking into, as it needs very little water and does well in the shade and in your climate. Look online for pics and maybe check it out at a nursery to see if it's the kind of plant you'd like in your woodland landscape.
Epimedium does well under trees and needs only moderate water. It might be worth looking into.
Vancouveria looks a bit like ivy and makes a nice groundcover in shady areas and actually prefers acid soil, but it needs moderate to regular water and "spreads slowly", unlike ivy. I guess it might come down to how quickly you'd like to see results.
