I use a server power supply like this to power the cards and the risers for up to 8 cards.
http://www.parallelminer.com/product/hp-1200-watt-power-supply-kit-for-gpu-mining-platinum-94-zec-dash-eth/
Then I use a ~400w PSU for the motherboard and SSD.

You also want to use PCIe 6 pin powered risers, like this:
http://www.parallelminer.com/product/ithoo-usb3-0-pci-express-1x-to-16x-extender-riser-card-adapter-w-24-cable/

Then use a GPU power splitter like this to power both the card and the riser:
http://www.parallelminer.com/product/18awg-pci-e-6pin-to-dual-8-pin-y-splitter-extension-cable-2x-62pin-cable-6in-each-side/