Species of native azalea offer a variety of colors, heights and sizes, fragrance and the possibility of almost continuous bloom from late March through September. Native Azalea bloom times. There are also a lot of interesting hybrids available. If the azaleas you have currently bloom well in the conditions/light you have why not add others with different bloom times, colors? There are a lot of interesting Kalmia hybrids to add to what you have too.

Sounds like you already have canopy, understory and shrub layers. Were you just looking for ideas for herbaceous stuff? Ferns are a great "foundation" for any woodland garden and there are many to choose from.

As far as interesting, this time of year I always think of Bloodroot, Virginia Bluebells, Hepatica, Spring Beauty, Iris cristata, shooting star. Wood poppy is another good one and you can keep it blooming if you water it. Jack in the pulpit (Arisaema) is interesting too and there are a lot of "new" ones coming to market if you like exotic stuff. Seems like your soil is probably slightly acidic which presents some interesting possibilities.

Gene Bush at Munchkin Nursey always has some cool plants that give me ideas for my gardens.

Sorry for the long post, guess I'm dreaming of my gardens and spring.

Wow! Thanks for the Native Azalea bloom time list. I'm Trying to find Large 36" or better evergreen ferns. Most of the Mountain Laurel and Blueberry is very rangy. I've picked out a few better Laurels to wack on and encourage bushing out. But, Lurels are very fussy here (at least). One year they look great and the next year (no kidding) I'm looking at a giant dead bush. Canopy is quite thick definately full shade in most areas, dappled to mostly shady in others. Yes, soil is acidic.

here are a few that i am growing in similar conditions:
oakleaf hydrangea
japanese maples
agarista populifolia (florida leucothoe)
camellias(you could try some of the cold-hardy selections)
pieris japonica and p. floribunda
mahonia bealei
various nandinas
taxus x hicksii and t. densiformis

Maybe Polystichum munitum? Western sword fern.

It's evergreen, gets about three feet and can take deep shade and a ph as low as around 4. Likes a bit of moisture. Bonus, deer won't touch it. I'm sure there are others. I like Christmas fern too, smaller though.

Oh! Just thought of another...

I think Dixie wood fern might be evergreen where you are (it isn't here) and it can get really big. I don't think it needs as much moisture as a Western sword fern either.