What I'm suggesting is a younger woman of African decent with reasonable to strong moderate to conservative credentials.
I have read someone speculating that Bobby Jindal might be a good match -- although I don't know if a Governor early in his first term would be a good choice or not, but probably no worse than anyone else without existing national name recognition. (As an aside, I was in India when he was elected Governor of Louisiana so I saw the coverage there. I'd be interested what it would be like if he was nominated for Vice President)
The other name I remember reading, and I think this was an article linked from a blog post at the Albuquerque Journal the other day, was Heather Wilson, who has represented the Albuquerque area in congress for ten, or so, years; but stepped down to run for the Senate. (She lost to the congressman from Southern New Mexico, who will now run against the third congressman from New Mexico for the Domenici's Senate seat). I think she was suggested as a younger woman with good moderate credentials.
Of course either choice suffer because they come from smaller states also in the southern US, although only Louisiana is considered as part of the "South."
One last wired thought, what would happen if McCain picked Wilson as his running mate, and then Obama picked Bill Richardson. Would the State of New Mexico become politically torn up as two of its residents were running against each other for national office?