If you into Ocing slightly, I would recommend a 550watt name brand like Corsair, OCZ or Antec ect. to be on the safe side. 400watt should be good for stock, but don't go out and get any PSU, Make sure there is enough amps on the 12v rail(s) and its known to be some what decent.
I was thinking about this Antec EarthWatts EA-500D Green 500 Watt 80 PLUS BRONZE Power Supply... or this Antec High Current Gamer HCG-400, 80 PLUS BRONZE, 400 Watt Power Supply . There is a 10 dollar price difference.