Simply take a look at the layout of the expansion slots for the prospective motherboards. There should be a top down view of the board. Since the 480s are usually dual slot, there should be at LEAST a slot between the pcie x16 slots, which can be anything. Best case scenario, there is space between the cards. This would need an extra slot between the cards (so 2 slots between the pcie x 16 slots).http://us.msi.com/product/mb/P67A-GD65--B3-.html
Look carefully at this. You need this kind of layout to have optimum cooling for multi GPUs.