A power supply of 450W+ with a native (ie. no 20->24-pin adapter) 24-pin ATX power connector from Enermax, Sparkle/Fortron, PC Power & Cooling or OCZ are going to be your best bets.
Avoid any unit by Ultra or Q-Tec, as these are known to be problematic units and probably not up to code. They are not recommended for any system (I wouldn't even pair one with a 300MHz Celeron system). There's been one review that I know of where an Ultra power supply blew up during a heavy load test. HWF has seen several Q-Tec units that have been the cause of problems.