Because of zone differences, my favored combos would probably not work for you :-) Have you looked at Traci DiSabato-Aust's The Well-Designed Mixed Garden? This is a great text for designing and developing a mixed perennial/shrub border and offers a great many stunning combinations to choose from. There is actually an 'encyclopedia' of plant combinations illustrated with photos. And since she is based in the midwest, much more zone appropriate choices.

One possible combo she outlines for part shade is Hydrangea quercifolia and Actaea (Cimicifuga) 'Brunette'. To that I might add Heuchera 'Green Spice' or Epimedium rubrum and perhaps Carex 'Ice Dance'.

Book should be in your library or local bookstores or you can order online.

I know this is not my topic...just jumping in here...but good suggestion on the book.

By no means am I advanced with combos but here are a few I like in my garden. I'm just starting to work more perennials in the designs.

Ivory Halo Dogwood with Purplicious Speewell
Northern Accents Ole Rose with Mammoth Pink Mum
Summerwine Ninebark with stella daylily
Tardiva Hydrangea with strawberry candy daylily

I've enjoyed the Hydrangea quercifolia and Actaea (mine is 'Hillside Black Beauty') that gardengal mentions for about 6 years now and they were definately meant for each other. Hostas and painted ferns round out the area for me, but I have a bit more shade than you do.

tj

From a designer's perspective, the best plant combinations involve a careful balance of contrasting and complimentary features. The 'contrast' part typically involves the use of plant shapes and foliage textures while the 'complimentary' aspect generally relates to colors as well as sharing similar growing conditions.

In the combination above, the bold, heavy texture of the hydrangea foliage is offset by the lacier, more delicate Actaea foliage. You also have the spreading mass of the hydrangea in contrast to the more upright, clumping form of the Actaea. The grass (Carex) adds still another form and textural contrast, while the smaller, rounder and spreading form of the heuchera or epimedium provides yet another textural effect. The hosta in tj's example does the same.

Much of the complimentary effect comes into play with the colors involved.......the deep maroon of the Actaea foliage compliments the deep green of the hydrangea and will accent the hydrangea as begins to turn into its fall colors. The heuchera picks up both of these colors, as does the painted fern or the epimedium as it puts out its new spring growth. And of course, all these plants enjoy similar growing conditions as well.

Because flowers are such a transitory aspect of a garden design, I tend to place less emphasis on combining specific flower types than I do on the foliage, but the above plants do offer a very nice combined flowering effect as well - the shape of the hydrangea blossoms is somewhat repeated in the spikes of the Actaea, plus the coloring of the coloring of the hydrangea flowers as they age will pick up the pinkish tones of the Actaea as well. And the heuchera or epimedium will offer an early and very delicate flower effect, repeated later by the hostas.

IMO, the best combinations involve at least three different plants and often, more. Less than that and you do not achieve enough contrast and compliment to make the combination really effective.