In 3.5e one of the strongest builds I'd ever seen was a hummingbird wild shape air-domain caster druid with the natural spell feat (I believe that is what it was called). They'd fly around the battlefield in bird form which gave them such insane AC bonuses as to be basically unhittable, then they'd just cast Call Lightning and Ice Storm and destroy the enemies while remaining untouchable. It was honestly insanely OP