Any quality 500-550 should give you more then enough power for your system.
It is important to know that a pc power supply only takes as much power as it needs so even a 800 watt power supply would not waste much more power(maybe even less if it a higher efficiency one). Just for example, My media center has a 300 watt power supply and pulls about 40 watts idle(right now) and my gaming system has an 850 watt power supply that has yet to pull much over 350(and to get that I have to push it way harder then just gaming).
Now you also should know the biggest thing you want to see is how much power the unit can deliver on its 12 volt rail(combined[not just adding rails] rating for multi rail units.).
Well that moved quick