It will run fine on any great quality 500, any good quality 550, and pretty much any 600+ that at least isn't some piece of junk. Most people vastly over estimate the power usage of a machine, but with a power supply it's not like it really matters since the bigger you get doesn't really change how much power your machine uses, just how much power you have available to use.
If you look at Anand's test rig for instance their total system consumption from the wall with a 780 was 365 watts. Assuming their power supply was 90% efficient that means the PSU was supplying just a shade under 330 watts to the machine.
That means even something like the
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139027 (Corsair CX500) that is rated to be able to push 456 watts on it's 12v line you'd be running at about 70% capacity (assuming every single watt is going down the 12v line, which is not the case).
Essentially, what I'm trying to say is just find a good quality supply that you like in the 500-650 watt range. Lots of people recommend the XFX 550w since it's made by Seasonic and a pretty solid supply yet pretty inexpensive.