What kind of space are you trying to fill? What about foliage with some color?

It is probably a 15' by 5' area. Colorful foliage is ok, but flowers are even better.

Astilbes are a fluffy type flower, Pulmonaria has flowers but mostly they are for the foliage same with Hostas and coral bells (Heuchera). Some thymes will deal with shade and they flower a little(like variegated lemon thyme has small pink flowers). Forget-me-nots(blue), Touch-Me-Nots(orange) and Columbines(pick the right one some are nothing to look at but some are really nice)
Siberian Irises might deal with some shade. Lily of the Valley, Solomen's Seal, monkshood, bee balm, bleeding heart, deadnettle(lamium),Jacob's Ladder, Lamb's ear, loosestrife, hellbore, foxglove.

Oh and I saw someone in my town who had an Azeala(hydrangea) in full shade FLOWERING!! I believe it was something like bright lights or orange bright lights-Manderin Lights that's it. They also have them in light pink, yellow and bright pink(the nursery here had them this year can't remember their names) and they have a light fruity smell.

Hope I helped some.

Lamium maculatum blooms all season.

Many of the hybrids of the native bleeding hearts bloom for a long time.

Almost no perennials bloom all season in our zone 5. And none that are what I'd call showy. For all-season color, I supplement my shady perennials with annuals such as impatiens and browallia, an underused and terrific annual.

alyciaadamo, that should be rhododendron, not hydrangea. Hydrangeas aren't related to azaleas, although there are many lovely ones.

Smilacina racemosa(unbeatable in all respects), Cimicifuga(all of them), Actea , Trilliums, Primula elatior, Geranium phaeum album, Podophyllum, Lilium martagon, Anemone nemorosa, Kirengeshoma palmata and koreana, Rodgersia, Brunnera,Uvularia, Disporum flavens, Gentiana asclepiada, Veratrum album and nigrum, Clematis macropetala, Clematis alpina, Meconopsis cambrica, Asiatic lilies(but fewer flowers), Oriental lilies.

Combination of all these plants will provide flowers through the whole season in heavy shade.

All the above plus Anemones will give you blooms in the fall, too. I have mostly Honorine Joubert, but there are lots from which to choose.

Astilbe really like moisture or they fry, even in shade. The ones near my bird baths do best because I dump the water every day when I put in clean. Hosta are addictive and I think I will never have enough.