Favorite native trees in northeast Georgia: Serviceberry, Sourwood, Fringe tree (the native one, Chionanthus virginicus, not the chinese one), bigleaf magnolia, southern magnolia, Tulip poplar (Liriodendron tulipifera), Eastern red cedar (Juniperus virginiana), paw paw (asimina triloba), wax myrtle.

Favorite native shrubs: native azaleas, mountain laurel, vaccinium (blueberries, lots of different ones), virginia sweetspire, sweetshrub (the species and the cultivar 'Athens'), Florida anise (illicium sp.), clethra, viburnums (nudum, dentatum, acerifolium are some of the native ones).

My suggestion for 4 season interest is to plant a variety of things: some flowering, some evergreen, some deciduous (and it is the deciduous ones that give you good fall color).

If you haven't already, I'd suggest you join the Georgia Native Plant Society and start participating in the metro area rescues. It's a good way to learn more about the natives in this area and to rescue some of them for your own garden.

Here is a link that might be useful: GNPS site

I have a Hardy Begonia that is in part sun and it does well. I like it's color as much as I do it's flowers. I think you'll find some discussions of it if you do a search of this forum and the Southern Gardener forum.