What PSU do you currently have? What's the budget for the new PSU? I'm guessing you would like to leave the option of SLI open since you have an Nvidia GPU and an SLI motherboard. I would recommend this PSU:Antec TruePower New TP-750 Blue 750W 80 PLUS BRONZE Certified Active PFC Power Supply
$104.99 w/promo code tp1505, ends 5/31 - $20 MIR
You certainly don't want to go cheap on the PSU. It's the most important component for a stable system.