You will need a Z77 based motherboard in order to overclock the "K"
Past that, most any will do.
If you want a very small case, look for a ITX or M-ATX sized motherboard.
Otherwise, pick the cheapest motherboard from your favored brand.
This ASRock Z77 Pro3 @$80 after rebate would be one of the least expensive: http://www.newegg.com/Product/Product.aspx?Item=N82E168...