mmm, I say stick with the better brands like Antec, Enermax and Coolermaster. i dont trust Aopen.
There is a big price jump from 550W upwards. and you are likely never to use more than 400W of it.
My Quad core Q6600 + 8800GTS with 7 hard drives only uses about 370W under load. Go for the best quality rather than the highest wattage. I'm running a old Antec Truepower 2 480W on mine.
Here is a few I would recommend. if you are in Cape Town, i can even supply you with them:
Enermax Liberty DXX 500w ( 12v : 384w ) , all-in-1 for ATX,EPS12V,BTX , High Efficiency , with modular cables + storage bag , active PFC , 20/24pin + 2x4 or 1x8pin 12v AUX , 2x6 or 1x6+1x8pin PCI-E power connectors ( 8 pin for for pci-e 2.0 vga card ) , 12cm thermal controled fan , support upto 18 drives , EMI shielding , dual 12V rails ; with OCP , OLP , OVP , OTP , SCP , UVP protection - 3 years warranty
about R1165 incl VAT
Antec TruePower Trio 650w ( 12v : 624w ) , SLi certrified - 650w , 24pin ( 4pin detachable ) , dedicated output circuits for 3.3V, 5V, Tripple 12V rail + voltage feedback detection + antec Low noise technology ; 2 x 6pin PCI-E 1.0 power connectors , 1x 120mm double ball bearing fans with advanced thermal control ; with OVP, OPP, SCP, UVP safety standard - 5 years warranty , SABS approved
about R1310
The Enermax would be my pick unless you go for a double 8800 graphics PC, then I would go for the 650W Antec.
Slightly better value is this one
Coolermaster RS-520-ASAA Real power 520w , EPS12V V2.91 + SSi + ATX 12V V2.3 , Modular cable manafgement , active PFC + 2x6 or 1x6+1x8pin PCI-E power connectors ( 8 pin for for pci-e 2.0 vga card ) , 24pin ( 4 pin detchable ) + 4 or 8pin 12v AUX , 1x 120mm fan with intelligent fan speed control ; with OVP , OTP , OCP , OLP , SCP - 3 years warranty
about R1125