Woodruff, Lilies of the Valley

I had no luck with my ferns but did plant blue mist flower this spring and it's my current favorite. Downside is that it spreads quickly and can become a pest.

I can vouch for it spreading quickly. I don't view it as a pest yet, but I may next year.

weedblock** Autocorrect =\

Woodblock and mulch over....problem solved...unless you prefer flowers over the empty spaces

While not native, there are some beautiful epimedium that fit the bill (aka barrenwort, bishop's hat, etc.).

Thanks everyone! I'll research those plants and give a few of them a try. I've always loved ferns. I love hosta too but in my experience the deer chomp those down.

I don't think roots are a problem under the tree.

Ferns. Here's a list a native varieties: https://www.nps.gov/plants/pubs/chesapeake/ferns.htm

For flowering plants--all native, widow's tears, trillium, common blue violets, bell flower, toothwort, trout lily, toad shade (all prettier than they sound), spring beauty, bleeding hearts, shooting stars, mist flower, dutchman's breeches, straw lilies, common boneset, white wood aster, hepatica, Canada mayflower, false Solomon’s seal, bishop's cap, many phloxes stonecrops, hellebores, and lobelias, jacob's ladder, jewel weed--great for humming birds love the shade.

Native shrubs--checkerberry, black huckleberry, winterberry, viburnum, dogwood, buttonbush, summer sweet, dangle berry, hydrangeas, sweet spire, inkberry, witch hazel, fetter bush, spice bush, bayberry--can all be understory plantings.

For more on their planting conditions: https://www.nps.gov/plants/pubs/chesapeake/pdf/chesapeakenatives.pdf

Is the soil compacted due to tree roots? If that is the case it is very difficult to get anything to grow there and you may be better off just mulching. We had this issue under a large silver maple.
If tree roots are not the problem, invest some time and effort into improving the soil before planting anything. Here are some suggestions for native groundcovers:
http://dnr2.maryland.gov/wildlife/Pages/habitat/wagroundcovers.aspx

Ajuga (carpet bugle)

Ferns? I have a similar area and they are doing great. I guess you wouldn't consider them to be ground cover, but they are keeping the weeds at bay, for sure.

Hostas and ferns are my "go to" plants for shade but I don't have to worry about dear (rabbits on the other hand).

I have a lot of blank spaces in my flower beds. As a result, I tend to have a lot of weeds. The previous owner of the house planted some nice shrubs like azaleas and lilac but 4 years later, the most of the shrubs are still tiny. (I think because the soil is so bad and they may have not been ideally placed regarding sun needs.) I have plans for the flower beds that get the most sun (and the most weeds) but I'm not sure what do with the beds up near the house which are more shady or part-shade. And there is an area where a tree has grown so big, it has shaded the rose bushes planted below it and they've died away.

I'm thinking that perhaps what I need is some shade loving ground cover. I would need to be deer resistant and, preferably, do well in poor/clay soil. Any suggestions? Or am I completely delusional that a ground cover will help crowd out weeds?

Right now I try to keep the beds mulched but its a lot of work.