I am using an Antec Neo 550W. It has 3, 12V rails with dedicated PCI-E power x 2.
It is a modular PSU (unused power cables can be removed). There is some controversy over the voltage fluctuations. I have not had any.
(Testing a 6400 @3.2 w/ P5B-D)
500W with dual 12V rails will do it cleanly (OCZ, Antec, Enermax, Silverstone...)
[SIZE=\"1\"]E6400 @ 3.4 , Noctua 120
7900GT @ 670/1680 , VF900
2 x 1GB Patriot 6400 @ 425
WD SATA 250GB
Neo HE 550
P180 / G15 / MX1000[/SIZE]