AMD specify as below:
500W (or greater) power supply with one 75W 6-pin PCI Express power connector recommended
600W power supply (or greater) with two 75W 6-pin PCI Express power connectors recommended for AMD CrossFire™ technology. http://www.amd.com/us/products/desktop/graphics/7000/78...
You can get good brands like Corsair and Seasonic. They are more expensive that other brands with the same capacity but that is because they use good design & quality material for better performance & tolerance to overloading.
It does not really matter... Having multi rail does not make the Antec better than Corsair... Perhaps this will be useful: http://www.jonnyguru.com/forums/showthread.php?t=3990
"The bottom line is, for 99% of the folks out there single vs. multiple +12V rails is a NON ISSUE. It's something that has been hyped up by marketing folks on BOTH SIDES of the fence. Too often we see mis-prioritized requests for PSU advice: Asking "what single +12V rail PSU should I get" when the person isn't even running SLI! Unless you're running a plethora of Peltiers in your machine, it should be a non-issue assuming that the PSU has all of the connectors your machine requires and there are no need for "splitters"."