If you DO decide on a butterfly garden, I agree with Stone; a more "wild" type of planting is better suited for that. If you just want a garden that is attractive to butterflies, though, many flowering plants (maybe most) will serve that purpose, and you can have a more formal type of arrangement. The area that you describe does sound a bit brutal for many plants, though; near the south side of my house is quite a difficult spot for keeping a lot of types of flowers going. Especially since you would like it to be "low maintenance." I think sedum would be an excellent choice, and Echinacea (coneflowers). Maybe iris? Most of the flowers that I grow are in partly shaded, moist areas, pretty much the opposite of what you have there. I'd look for plants described as "sun loving" and "drought tolerant."
