The better answer is any motherboard that uses an X58 chipset would be good - or a motherboard that uses a P55 chipset with 1x16 PCIe socket. Do not buy a P55 motherboard if they offer 2x16 PCIe sockets - those run at half speed and the 5970 WILL be impacted.
I say X58 becasue you know it will work for you. You will have to be very cautious with a P55 system.
The ATI 5970 is the only graphics card that needs a full native 16 lanes dedicated to it.
Buy an X58 based motherboard based on features and cost you can find.