A quality 400W+ psu with 1x PCI-E will run your specs. Ideally it would be a wise investment to buy a 500-600W with 2 x PCI-E 6 pins if you ever decide to change your gpu. Don't buy junk! Antec,Corsair,XFX,OZC,and Seasonic offer reliable units.
At a minimum you should have a power supply with a combined +12 Volt continuous current rating of 24 Amps or greater and it should have at least one 6-pin PCI Express supplementary power connector.
Total Power Supply Wattage is NOT a crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important.
Thanks for the advice, everyone. I'll look for a PSU that fits into those parameters.