This thread gives some info and tips about the most popular boards. It's made by overclockers but I think some info is relevant for all S939 buyers.
Check it out!
S939 mobo guide & A64 P-rating article
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee
BeHardware compares most of the Athlon 64 CPUs (both socket 754 & 939) available and shows how much you can trust the P-rating.