What you will need is and Intel based Northbridge chipset motherboard that supports Crossfire and has 2 x PCI Express 2.0 x16 slots. It will also have to be a motherboard that takes an Intel processor. Here is a nice board for a good price and will support Crossfire. http://www.newegg.com/Product/Product.aspx?Item=N82E16813131299
Your best bet is to go with an Intel chipset. Any mother board with the P45, x38, x48 will be a great choice. Asus makes awesome boards and the one recommended has tons of feature for that price.
I just finished a build with an ASUS Rampage Formula, (great board), and just ordered a P5Q Pro to build for my Wife's work. Looking foward to another ASUS build. Be sure to check the approved vendors list when choosing RAM though.