I use a combination of 2 cups corn meal, 1 cup corn flour (commercial fish fry like Zatarains), and a half cup corn starch.  You can season it with salt , black pepper, lemon pepper, garlic powder, and cayenne, how ever you like.  This is also a good blend for frying oysters.  If you fry whole fillets don't fry too hot so the exterior gets crispy brown before the fish is done.