it all depends on what else you're going to have on your mobo. 600W can be enough, unless you're going to have massive amount of other stuff in your rig.
but for a decent setup, 600W~ish is usually plenty.
anything in this area of powersupply would usually do enough 601-700W Power Supplies - Electronic Inventory Online
if youre planning to have a SLI/CrossFire setup, i suggest you get a PSU with more power, just a suggestion :P beefy vcard can eat up a lot of wattage.