Celestial WArrior:
and not sure...Thinking Skills and powers has revised options for kits?
I would stay well away from
Skills & Powers, it was a broken system that was too easy to meta-game.
On the other hand, the two other books from that series are much better.
Combat & Tactics had some interesting combat options, even if you didn't want to expand to using miniatures. It certainly made playing a fighter worthwhile. And
Spells & Magic would be completely essential to a Planescape game -- the alternate magic systems could represent different factions and planar cultures.