I try to not use 3E material for PF builds, because it just opens the floodgates and makes a lot of stuff seem pointless. Lion Totem Barb 1 alone makes many build ideas obsolete, for example.
But the thing on the top of my list if 3E was allowed would be Elusive Target. Negating power attack and making friends ill each other alone is sexy. Tack on the whole "anyone who misses you on an AoO for movement you can free action (NOT an AoO!) trip, leading to more AoOs on top of the one you got from Snake Fang for them missing you in the first place, and how could they when you've got an extra +8 Mobility AC," and... *drools*
Ahem, but yeah. Already feat starved, couldn't fit in Fury's Fall (add dex to his tripping for another +7) and Vicious Stomp (another AoO from trip) as it is. I guess it's less of an issue if 3E material (flaws) is allowed, though.