Which species are the best for nectar production?
Check out bi-color lespedeza for ease in establishing and drought tolerance. Bees love it, very hearty, and long lived, and it reseeds it's self too. Also bi-color makes good cover for other wildlife. Cow vetch and hairy vetch grows well here but I don't know about where you are. I also no longer remember the difference between the vetches since now days no one plants vetch anymore because there is no government subsidy, commodity, marketing, or loan program available to encourage farmers to cultivate vetch. Now if you started a whispering campaign along the lines that smoking vetch got you high that might change.