I'm not sure you want a real "ground cover"......maybe just a low, spreading perennial that can fill in the blank spaces. The lamb's ear (stachys) could work but so could Veronica 'Georgia Blue', Helianthemum (sunroses), various creeping/spreading campanulas, Iberis sempervirens (candytuft), heaths or heathers, hardy geraniums, etc. In zone 7, there are literally hundreds of different plants that could work. Visit your local retail nursery/garden center to see what they offer and looks good to you.

You've gotten some good plant suggestions so far, including to do a mixture, which is usually my preference if the area will be visible. T2D's front slope mixed planting is gorgeous. Perhaps she'll add a photo or two. Vinca should be fully hardy for you since it is for me. However, I find it crawls over my barrier (a 5" deep band of edging material with a row of bricks alongside) and roots in the lawn, so I wouldn't recommend it. This might be a good spot for variegated bishop's weed(Aegopodium), which is normally a pest since it doesn't play well with others, but if you want just one kind of plant, put a barrier around the bed and it should be OK. You could plant bulbs to come up through it. This might be evergreen for you, not sure. Ajuga would work and you could try some of the more resiliant coral bells(Heuchera) I have a rather steep bed in an area behind the house that isn't in our normal traffic pattern that I needed to fill quickly to prevent erosion, and since I had a bunch of the old-fashioned daylilies that I had dug up elsewhere in the garden, I used those. I'm now adding a few shrubs and other hardy perennials that I think will be willing to duke it out with the daylilies. Old-fashioned daylillies aren't evergreen, but they might be something you'd want to throw into a mixed bed as they are fine with full sun and don't need lots of water. Regardless of what you end up planting in the bed, prevention of weeds while your plants get established is really important. You want to kill everything that's currently growing there, whether by smothering it (do a search for lasagna gardening) or by covering it with black plastic for a couple of months or whatever method you choose. After planting, you might want to put down corn gluten which will discourage seeds from germinating and then a heavy layer of mulch on all the bare soil areas both to keep moisture in and prevent light from reaching the weed seeds and bits of roots that are in all soils and will sprout with light. Mulch will also prevent erosion until the soil is covered with plants and make any weeds that do come up easier to pull. Also, install your outer barrier either before you plant or just after since if you delay and grass crawls sideways into the bed, you will battle it forever. Here's a previous thread that might help you out: http://forums.gardenweb.com/forums/load/neweng/msg0317034129496.html Here is a link that might be useful: New England groundcover FAQ

What kind of sun exposure does the slope get? There are a myriad of possibilities range form vines like vinca minor or pachysandra to low-growing ground cover shrubs like some creeping junipers or cottoneaster, etc. Slopes can also be terraced to plant perennials if desired. One of my sisters has a slope to her driveway where it borders her neighbor and she put some junipers along part of it and hosta on other parts, and these have been filling it in nicely. Again it depends on what the sun exposure is regarding certain ground covers (some prefer shade). Of course laying down sod is another possibility.

We too have two steep hills in our backyard that get barely any water. We're in north GA. When we bought the house there were clumps of English Ivy, obviously doing terribly. You could see the awful erosion all around the clumps. We planted the spreading type of liriope two years ago, and let me tell you we planted three hundred clumps and five have spread so far. We planted the orange wild daylilies here and there, they have become huge and have started to spread. I stuck giant daffodil bulbs and some vinca minor in spots, they are both doing well so far. I will tell you I have creeping phlox out front with good soil and water, and it has covered everything it can reach (hard to weed in). I stuck two of the same plants out back in a corner of the hill to see how it did, and both are the same exact size two years later. Just my two cents to add, hope I helped!