i would liek to point you to Rokugan campaign setting
in the feats section there are 2 feats of great use to a power attacker
Way of the lion
+2 bonus to attacks vs people with armor or NA but no more than there armor or NA, can be taken multiple times
and
Akodos technique
If you succeed on a melee attack greater than your opponents ac, then you add the excess/2 to your next attack
don't know if its been mentioned before but i find the use of this pair of feats to be of rather nice function