I'm not sure if you can keep rosemary under a foot tall but it would be worth looking into. It looked good all year long in my neighborhood.

I mostly see this plant in baskets or beds, but a few years ago I was stunned to see it as a groundcover in a small front yard. It's a great plant, does well in this zone, doesn't require a ton of water and is a beautiful foil to green. Check out the links in this thread for some good pics.

Here is a link that might be useful: Purple 'wandering jew'

Second the Tradescantia Pallida Purpurea, and you could mix in some Portulacaria afra. I think the two would mix well, you'd have green and purple, they can both be kept low growing and low water, they can take shade, the heat, and the cold. The "elephant's food" might nip back a bit if it freezes, but it recovers. You would have to cut back once in a while to keep it low. Some varieties are trailing which would work best as a ground cover.

Not sure where you are, but in Tucson, lantana won't reliably stay green year-round. Plus, I hate it :)

I am a great fan of mexican primroses and they would do very well in the area you describe. put some stepping stones thru the area for a walkway and plant primroses on each side of it.
lots of people hate primroses because they are hardy and keep coming back. they don't have thorns or stickers and they make lovely soft pink flowers. if you get tired of them you can cut them off at the ground and they'll be gone for awhile.
I consider them "the grandma plant"
when I got too old to do all that digging and transplanting and etc etc etc.. I just let the primroses go and have not been sorry. they are beautiful...

What a great idea, I love those delicate light pink flowers too. I have just the spot! Thanks amijo.

I like all these ideas! I think I'll create a few different sections for different ground covers instead of trying to decide on just one. The space is plenty large enough. On another note, I just received some Wedelia cuttings I ordered on ebay. so excited to get them in the ground under my ash tree, but today is just crazy windy and dusty :( Hopefully it dies down soon so I can get out there!

I have some mexican primrose growing in my front yard, with my roses. I'm not sure how it got there; I must've planted them at some point...I love them, they are really pretty and don't seem invasive to me. Mine die back when it gets hot.