I think your best bet is a mix of shrubs and small trees that are OK in some shade - not planted in a line, but like woods: one here and one there all the way to the drop-off.

Five easygoing natives that grow well in this area are cornus florida (dogwood), cercis canadensis (redbud), lindera benzoin (spicebush), hamamelis virginiana (witch hazel) and calycanthus floridus (sweetshrub). You could underplant with ferns, mayapple and hellebores and provide yourself with a zero-maintenance "step-down" from 70-footers to smaller scale plants. It will still have a woodland (jungle!) look, but I think you'll have to learn to like that because of the big trees.

Good idea, Leslie. I'd add hollies and small yews as well.

You might enjoy a few Kerrias. They do well in partial shade, and get about six feet tall. They will spread over time, perhaps too much in rich soil. They are clump forming and develop fairly rapidly from the center, with straight, long, rather weak green stems that have attractive small lance-shaped flowers, with yellow blossoms along them in the early spring.

Oakleaf hydrangea will eventully get to six feet or so, and can be quite attractive. It, too, has weak stems which can break fairly easily.

Forsythia would be another option; it also does well in partial shade. Both lose their leaves in the winter. but eventually their stems get dense enough to still have a screening effect. (The Chinese have a strain of Forsythia bred to have antibiotic properties in its buds...)

If you have the room for it, a doublefile viburnum--or even a miniature one--provides excellent screening, and the leaves tend to winter over. That would look good in one back corner.

Yews do well in partial shade and can be purchased inexpensively from the big box stores. They develop well and can be put in quite small; in a few years they will put on quite a bit of growth. There are vertical, round, and horizontal strains, and a mixture of these types can be quite attractive. They can have a good appearance without pruning. They all can become quite large eventually. The foliage winters over well, but is so dark that you may find an exclusive planting of it gloomy. The birds can eat the fully ripened fruits, but the seed and foliage are toxic.