I love Celandine Poppy (Stylophorum diphyllum)-- nice foliage, and yellow flowers that really pop in a woodland setting. I also love Virginia Bluebells (Mertensia virginica)-- outstanding blue flowers on this ephemeral. Another favorite is Indian Pink (Spigelia marilandica) -- bright red flowers are a real standout.

I really need to get some of those Erythroniums. so pretty!

Rue Anemone (Thalictrum thalictroides) is one of my favorites and I find it can be especially long lasting and very adaptable.

Hepatica is a favorite because it is the first thing to bloom for me. It does best for me when planted near the base of a large tree.

Of course I like the things that have already been mentioned ... but I wanted to offer up some other suggestions.

Here's a few more that I like.......
Spring Beauty - Claytonia virginica, C. caroliniana
Columbine - Aquilegia canadensis, A. chrysantha, A. vulgaris (Introduced)
Twin leaf - Jeffersonia diphylla
May Apple - Podophyllum peltatum
Atanasco lily - Zephyranthes atamasca
Moss phlox - Phlox subulata
Lady-slipper Orchids

And the Iris.....
Iris cristata - Dwarf crested
verna - Dwarf violet
versicolor - Harlequin blue flag
hexagona - Dixie (wish mine would bloom, just once!)
pseudacorus - Pale yellow (Introduced, but I still like it!)
Rb