There are Southern gardeners here with more experience in your climate... but Rattlesnake and Purple Pod Pole sound like good choices. Both are snap beans.

Concur, altho Pole purple pod is a bit more heat sensitive than many. Ferry Morse carries an excellent selection of beans, but not all will be available at many outlets. In pole beans they carry Kentucky Blue, Kentucky Wonder, Romano, , Trianfo Violet, Blue Lake, Rattlesnake. They also have a good selection of bush beans including Amythyst, Royal Burgandy, Landreth's Stringless, Blue Lake, Contender (my favorite), Derby, Green Crop, Provider, Burpee Stringless green Pod, Harvester, Tendergreen, Top Crop etc. http://www.plantationproducts.com/catalog/cfCatalog.cfm?c=3008

I have not had luck with purple pod in Central Texas. Rattlesnake been are very heat resistant and prolific. They freeze well.I am trying provider and dragon tongue this year. So far the new ones seem to be doing great but we have only gotten to warm and humid so far. It is in the 80's still. No 90-'s and 100. I grew rattlesnake and it held it own the year it was 100 for a while but I shut my garden down early that year. The watering was phenomenal. I did get a crop.