Your suggestions seem to be large leaved plants? Is that what you are looking for? Could just be coincidence because dense-dense shade would likely produce large leaves.

How about waxbells? Kirengeshoma palmata --
I think they can get big. Not sure how they would do in dense-dense shade. Mine get morning sun.

ALso cimicifuga can get big but seems to take awhile.

How about a shrub like pieris or yew (gasp) or holly?

If you get them off to a good start (water/soil) the first year or so, they should be okay in dry conditions.

Not sure that Gunnera would survive in zone 5. Ligularia maybe?

Ligularia dentata is a great suggestion - it's the toughest of the bunch, when it comes to large-leaved perennials. (I've tried them all over the years, and this one has consistently done well where others have petered out.)

I have one in particular that I love, called 'Dark Beauty' (aka something like 'Dunkelaubig', although I can't find it under that name any more with Google.) It thrives in fairly deep shade on the north side of a line of spruce that's faced down with some hefty Euonymus kiautschovica 'Manhattan' - it's dark and somewhat dry there.

That Euonymus might also be the kind of thing you're looking for - tough as can be, and can be trimmed to any size - if you're interested in a lax shrub for this spot.

I have darmera peltata - and planted it in a wallow after seeing some great specimens growing in a swamp in a botanic garden. It really loves water, and wouldn't be happy in a dry location.

My Kirengeshoma doesn't seem to have much mass, although I suppose it's actually fairly big - maybe large-leaved perennials just convey themselves as bigger. Mine also gets some sun, so I'd be concerned about how it would fare in a really dark area.

I bought a petasites and planted it in deep dry shade when I realized it had the potential to be a problem if it was happy. I do believe it's dead, although it might still be hanging on - haven't looked lately.

Ooh, I just remembered. I have an enormous aconitum - A. carmichaelii I think - that got moved into the woodland garden because it was too tall for the original spot where I'd planted it. I really didn't expect much from it, but last fall it was LOADED with huge deep blue flowers and it seems really happy. Actually there are 2 or 3 of them out there, very slowly spreading. It's between a rock and a hard place (a Norway maple and a stockade fence!) and seems to be thriving. Very late flowers, very clean, deep green, slightly glossy foliage, and a real vertical accent. It's behind some enormous hostas and the contrast is quite nice, if I do say so myself. No staking, either.

Kirengeshoma would need a moist soil and will not bloom in a 'Dense Dense Dense Shade'.
Gunnera and Darmera are a typical waterside plants and will not thrive in a dry environment.
Contrary, Petasites wouldn't mind either or both of such conditions.

I wouldn't plant the Manhattan Euonymus unless you're a fan of flies. They are attracted to this plant by the millions.

what george said.(ego45). Plus:
persicaria lance corporal- fantastic plant

shrubs- lonicera and euonymus elata are tough as nails drought resistant/full shade tolerant.
maybe maidenhair and christmas ferns.

here is the section(not yet uploaded) on Dry Shade on our new website:
best,
mindy

CAPTION- Dry Shade Wasteland to Shade Hut Woodland
TEXT:
Dry shade is the bain of existence for many gardeners. We didn't come up against it until we developed a previously untouched area of elevated woodland that was under four mature sugar maples. Did I say woodland? I meant wasteland. Dry powdery nutritionless silt. I am happy to report that it is now the area you see in the photo above, complete with pond and waterfall and very few inches of visible ground.
We began by removing all the brush and weeds. We left only the maples and the fence lined with some red winged euonymus and wild honeysuckle bushes. These shrubs were useful because they had the requisite 'tough as nails' constitution to survive in these dreadful conditions and they were a green backdrop, hiding the fence. We knew we would eventually replace them but for now, they were helpful. Next we brought in tons and tons of compost and aged manure, working it in with pitchforks and shovels. If we had had shredded leaves (awareness) at that time, we surely would have added them. We wanted a rich base in which to give our gladiators-to-be their best chance at survival. We then tackled the mental design. We began with where to place a bench? >>> Up against the fence, facing towards the back of the house. We knew we wanted the cool sound of water so we then dug, lined, and rock edged a pond with small waterfall. Then we began planting. Hiding the dirt, creating a lush green carpet, was our big goal. We knew that the maples would continue with their mapledom, meaning their moisture and nutrition- sucking ways. So nothing completely crazy like astilbes that need constant moisture to do well. After many years of experimenting, our dry shade workhorses include, as groundcovers: lamium, lamiastrum, epimedium, Allegheny pachysandra, vinca, geranium machrorhizum, variegated bamboo, and holly. Holly? Well, surprisingly, yes. When we planted the two Blue Maid hollies by the short stone wall, we were hoping that they would tolerate the dryness and rise to bush form. They did handle the dryness just fine, but the lack of sunlight was another thing. They responded by growing only 15' tall, and their branches all kept reaching out horizontally for that elusive light. This resulted in very long drooping glossy dark green branches making for a visually rich and unusual groundcover . For medium height we added leucothoe, variegated solomon seal, uvularia, dicentra, bergenia, trout lilies, kerria Moonlight, and hostas. ( Laurel and pieris are surviving but not thrilled to be there.)Yellow flag iris(unpotted, bare root! ) continues as the resident pond plant.
As of 2009, 'The Maple Bed' changed once again. Disease took most of the sugar maples , so sunlight was finally able to enter the scene. We have planted a grove of assorted Japanese maples in their place, with a few medium height open-canpoied trees like halesia and styrax. Cledastris lutea, our one new tall tree, will soon be covered with glorious pink panicles.Flowering hydrangea vines are climbing the remaining sugar maple and the shade hut.

Here is a link that might be useful: The Cotton-Arbo retum

LOL, T.O. - yes indeed, when (and if) Manhattan blooms it is absolutely abuzz. The flowers attract bees and flies, but I can't say that it makes them (insects) multiply - we spend most weekends in our back yard and the euonymus hedge buzzes very loudly when (or where - mostly at the sunny end) it flowers. It's interesting, and it's the only place I see flies in the yard. Not a problem, in my book, especailly in shade where it doesn't flower heavily. The down side is that it also doesn't fruit heavily in shade.

For a shrub: I have a Calycanthus floridus ('Michael Lindsey') growing happily in dense shade with only an hour or two of barely dappled shade per day. Nicely fragrant dark maroon flowers. Has anybody else had good or back luck with the Carolina Allspice in dense shade?

Maybe also consider a Kalmia latifolia (Mountain Laurel), although you would think it would thrive in similar conditions to a Rhododendron. (Are you sure it's not a soil issue with the Rhododendrons?)

For a herbaceous plant: I grow a Kelsey's Coral Plume Poppy (Macleaya microcarpa) successfully in pretty dense and dry shade, and it can get really big. It's more commonly found in lots of sun in a cottage garden environment, but I have been pleasantly surprised with it in the shade. Go figure.

Ligularia requires wet conditions, so only use it if you like watering it often during the hot time in the summer.

I thought that Kirengeshoma (both K. palmatum and K. koreana) only grow to 4' high; not sure if those are big enough for you.

Thought of trying Aruncus dioicus (Goatsbeard)? Big and sturdy, although in deep shade it may flower only weakly (if flowering matters to you).

How about a super-big Hosta... like H. 'Sagae'?

extragalactic,
I have Keringeshoma in a dry(ish) part-sun and in a wet(ish) part-sun where both reaching 5 1/2-6'. In both cases they have 2 hours of sun by the end of the day. The only notable difference is that first one always blooms 2 weeks ahead of the second one and subsequently starts winter preparation 2 weeks earlier. They both sprouts at about the same time.

I've found that Ligularia only needs water if planted in sun - dry shade is where most of mine are, and they're quite happy. This is mainly L. dentata Dark Beauty, although I have one or 2 others (Desdemona, maybe?) that also seem fine without being watered.

How tall does Hakonechloa macra (hakone grass) get? Mine are young, mostly "All Gold" and they also seem to like the dry shade at the top of a small stone wall.

Hakonechloa 'alba striata' gets tall (3') and grows much faster than the original 'Aureola'

WOW!!! GReat suggestions!! I have an aruncus just about 2 feet away from this spot and it does well. Not wet enough for Ligularia. Had a kirengeshoma in another spot and it was fine, but I'm looking for something more dramatic. Will look into all the other ideas !
Thanks so much. Can calycanthus take zone 5 temps?

6' tall for Kirengeshoma? I planted a K. koreana last year thinking it will only get to 3-4'... guess I need to find a new place for it.

I've seen Calycanthus floridus listed as either zone 4 or 5.

As for Ligularia and watering: I find that L. dentata 'Britt Marie Crawford' (purple leaves) and L. stenocephala 'The Rocket' really need watering in the hottest part of the summer, even in dry shade, but that L. przewalskii does not. Your mileage may vary.

A dense shade surprise for me has been Caryopteris divaricata 'Snow Fairy', although only 2.5-3' a couple of them planted together will light up a dark spot like a 100 watt bulb.

"... will light up a dark spot like a 100 watt bulb."
Ditto.

I wonder if Kerria would work in a dark corner? Not as bright as a variegated shrub, but blooming shrubs in shade are nice too.

Depends on how moist soil will be.
In a watered shade my Kerrias are over 6' and about 3' at the base. In a dry shade they are just spindly 4'x1' bunch of twigs.
Cornus 'Ivory Halo' perharps?