From what I've heard the minimum power requirements for a GTX 480 is:
A minimum of 600W total system power.
A minimum of 42A on the +12V rails.
Obviously you need your PCI-E connector for your card too. Most high-quality PSUs that provide 600W will have more than 42A on the +12V rails. I would recommend Corsair primarily but others include Antec, Seasonic etc. Don't forget that the 42A is for the whole system not just your GPU so don't worry about that. It shouldn't matter whether your PSU has a single or multiple +12V rails as long as they provide the necessary amperage. If you're unsure of the amperage a PSU provides check the manufacturer's website or post back here if you're stuck. Any decent PSU manufacturer will have their ratings on their website.
I have a better recommendation. There has been too much speculation and a lot of unsubstantiated rumors. Let's just wait a couple of days for the official release. Most of the time a few technical reviews are published on the day of release. Wouldn't hurt to wait until we had solid information about system requirements and power consumption. This Friday is the big day. It is less than 48 hours away.
A +12 volt rail supplies power to the cpu, the video card, and some other components. The +12 volt rail delivers about about 75% of the power used by a system. There are other rails with other voltages that also deliver power to other components.
Here is a link to an excellent explanation about multiple +12 volt rails posted by Jonny Guru: