Most of the Mini-ITX boards available for either FM1 (AMD Llano) or Intel Socket 1155 (Sandy Bridge) will take 1 PCIe X16 card. This will be good for a single GPU system.
On the other hand the CASE that you plan to put that in is very important. For a high end GPU you'll need a CASE that will fit an ATX power supply and have a large space for the GPU card. I'd suggest This Lian Li or Similar: http://www.newegg.com/Product/Product.aspx?Item=N82E16811112265
It would help to know Intel or AMD processor, and then which processor/socket. And if the case the board is in can accept full-height cards or half-height. And if your PSU is adequate for said GTX card...
and what the heating situation is like in your case and how wide of a card you can fit and how much you're willing to spend and if you need any special features like built-in wifi
Most of the Mini-ITX boards available for either FM1 (AMD Llano) or Intel Socket 1155 (Sandy Bridge) will take 1 PCIe X16 card. This will be good for a single GPU system.
On the other hand the CASE that you plan to put that in is very important. For a high end GPU you'll need a CASE that will fit an ATX power supply and have a large space for the GPU card. I'd suggest This Lian Li or Similar: http://www.newegg.com/Product/Product.aspx?Item=N82E16811112265