A 500/600W power supply. A 600W would be slightly overkill, but would give you some overhead for upgrades. Stick with Corsair/Antec/XFX/PC Power&Cooling/Seasonic/Silverstone
I'm quite happy with my Corsair Builder's Series 600w PSU. Using it to run a Radeon 5770 and a Phenom II X4, which uses about as much power as an i7. Maybe even more.