this is the motherboard i've been choosing to use with rigs that have 2-3 cards in them.http://www.amazon.com/gp/product/B003IHUSAO
i have 3 5970s in one, spaced out so that they have room to breathe.
breathing room was a concern for me, because i wasn't putting the motherboard into a well-ventilated case,
instead opting to go with open air myopenpc's workbenches.
..not sure if that is overkill for you...
also, i would recommend at least an 800 watt psu from a more reputable brand, like coolermaster or corsair.
.. but i'm not sure about exact wattages to be honest .. you may be able to get by with that.
i know it takes at least 1000 watts to power 3 hd5970s. but that's double the gpus...