Depends on the rest of your setup. If you have top-end hardware, it will demand more power, meaning you'll need a better power supply. Can you post the rest of your specs for your PC?
I would suggest a 700W - 750W PSU...for a build like that, your PSU is going to be working about 80% of the time, and from my personal experience, I've been told that it's better to get a power supply that's high-end, so it doesn't always have to work under extreme circumstances. Less strain couldn't hurt...only your pockets.