When I had to relocate to a "northern clime" zone 7 from zone 9, I was really depressed in winter. I am adjusting better this year, and I have been adding winter plants. Here are some I have added and perhaps they would fit your situation. You may have to do some research on how big they get, or find some dwarf varieties. Pieris, camellia, various hollies (yaupon, Foster's, deciduous), regular and dwarf nandina, hellebores, Mahonia, carolina jessamine, cleyera, dwarf alberta spruce, ornamental cabbage/kale, violas, pansies, some herbs like thyme. Hope some of this will work for you. And, even though it is not December yet, my knockout roses look awesome right now and some other roses have blooms too.

3' X 12' is pretty small. You're not going to have much space, considering the other plantings. Generally winter interest comes from evergreen shrubs and trees or other shrubs that offer bark, berries or occasionally, winter flowers, but most of these will easily overwhelm a bed that size. There are some perennials that will hold their foliage through the winter and offer some sort of winter interest - hellebores, heucheras (coral bells), bergenia and a good many varieties of euphorbia come to mind. Also evergreen grasses like carex or variegated liriope (not a grass but close enough). And there's lots of evergreen groundcovers, including some, like wintergreen, that will change color during colder winter weather.

You might also look at dwarf conifers - many of these will stay very small and offer a range of colors and textures. Also 'Harbor Dwarf' nandina is a dainty, compact plant with great foliage color in winter.

I'm in GA as well... I have some Autumn ferns that have survived our most recent frost and have changed colors. I believe they are evergreen and look great year round. Pansies of course are the best flowers for the winter and snapdragons seem to do okay as well.

Here is a great blog post on winter gardening. A great blog that teaches you when and how to harvest your vegetables.

http://blog.mindbites.com/winter-gardening-tips-when-to-harvest-your-vegetables/

Here is a link that might be useful: Harvest Plants

Have you considered non-plant items for interest. My idea for a small space would include a bird feeder, birds flying in and out add lots of color and interest and don't take up much space.