Crossfire is AMD's term, and SLI is Nvidia's term for the same function.
The GTX 670 should work fine as a single card.
Start looking for Intel CPU motherboards and there are dozens to choose from. Asus, Gigabyte, EVGA, Asrock, etc.
Look for socket LGA 1155 motherboards.
Here is one example: http://www.newegg.com/Product/Product.aspx?Item=N82E16813157293
(please checkout a few other boards also).