http://honeylove.org/top-30-flowers-for-bees/
http://thehoneybeeconservancy.org/act-today/plant-a-bee-garden/
I know it want be enough to sustain your bees alone but with some care and love it might just help provide early and late nectar and stuff for your bees in a dearth.
I planted a patch of wildflower "Honey Bee Mix" last year. In my case, replacing grass with wildflowers was a multiple bonus - once a fall mowing, far less fertilizing & less watering.
It provided the bees with something to work all summer long, and me something to enjoy watching.
Fun stuff. I am working on something like that for myself. I know it will never be enough for them but it does help.
I just moved a citrus plant out by my bees. Very few native pollinators around my house for some reason right now. No honeybees moved on it soon but a big ole bumble bee did.