500W from a good company will be more then enough. The 660/TI/70 and 680 are all 150W-200W cards. Your CPU is another 77W stock. So even if you grabbed a GTX680 for the system you are looking at around 325W. As long as you are getting an Antec, Corsair, Seasonic, XFX, etc you'll be fine. Just avoid the Athena power and Diabloteks, etc.