Can already tell you from experience it runs fine on a Corsair AX650W w/ i7-2600K @ stock. The thing with purchasing a power supply also is that you need to factor in the efficiency curve.
Personally, I think 650 is all you need for non-OC single GPU solutions... I'd bump it up a notch if I was overclocking though.
A 680 runs fine on 650W PSU w/ i7-2600K @ stock too. The way things are going, for the most part, efficiency is where companies are targeting so depending on where you're wanting to go in future (SLI/Crossfire mainly) should dictate what you buy in a PSU.
Me personally? I'm a single GPU guy, so I don't see myself replacing my PSU until it breaks more or less... *knocks on wood* OR I decide to OC, in which case I'd like a 750W at least.