DFI Crossfire RD480 , just don't get rev 1 , rev 2 & 3 are the stable one. New egg is only shipping REV 3 which is awesome
Asus Crossfire board is cheap and has a beast hidden in its uglyness but it feature wise isn't so good.
1x X1900XT $520 now but in feb it should be $499 below
1x X1900XT Crossfire $600 now but in feb it should be $549 below
Good RD580 Board are coming out early feb :
DFI RD580 Crossfire <<< would be alround fav
Asus RD580 Crossfire <<< would be my fav if cost is no objective
MSI RD580 Crossfire