Your psu requirements are almost entirely driven by the graphics card/s you select.
Which one did you have in mind?
A quality 600 or 650w psu will drive most single graphics cards out there.
Quality units come from Corsair, PC P&C,Antec, XFX, and Seasonic to name a few. There are others.
The wattage is not as important as the amps on the 12v rails, and poor psu's do not deliver the wattage there.