Elusive target is from Complete Warrior. Requires Dodge and Mobility. a) if you dodge target power attacks, he gets no extra damage. b) if you're flanked by your dodge target and another, you can make your dodge target miss his first attack and stab his buddy instead. c) if you provoke an AOO for movement and it misses, you can get a free trip attempt on the attacker with no return trip.
Power attack I use mostly as a versatility feat, for rogues. He's got the strength for it, and a 13 bab at 18th level. It's not something you use every time, but when your sneak attack isn't working, your damage as a rogue is often very poor. Hitting the elder earth elemental for 1d8+6 with your longsword is not terribly effective. If you're not going to hurt it, you might as well swing harder and hope to get lucky.