Healthy 700W, I assume you mean a good quality unit then XFX,antec,Corsair(one of their better models) or Seasonic. Of course other units can be good quality too.
I might advise you to not spend all of your money solely on a GPU, you may see a benefit upgrading mobo/CPU/Ram, especially RAM to DDR3.
Your GPU isn't too bad and there may be a bottleneck is you stick an expensive card in like the GTX 770.