Having played a very-high to epic-level druid, wildshape ain't what it's cracked up to be. Very few animals have an armor class naturally above a 20, and if your DM doesn't allow that "wild" enhancement to armor or miscellaneous items, turning into wildshape means depending on NOTHING but the animal's and your natural stats. It's great that you have a 30 STR... until a high-level fighter or melee-monster gets within 5 to 15 feet of you...
Now, one thing I used to do was wildshape into a legendary form, and then use Nature's Avatar (9th level Spell Compendium spell) now THAT made me a combat monster -- however, WotC may have ruled at some point that Druids don't get the "Animal" subtype like it says they do in the rules, so that would be stifled.
Druids do, however, excel at powerful area-control spells, and they do excel at overcoming a creature's spell resistance, thanks to conjurations being their strongest suit. My favorite trick was to assume a fast flying form (eagle, legendary eagle, or similar), summon help, and let the help tear around the countryside. When I needed to cast some world-shaking spells, I'd light on a safe area, far from combat, and toss out some stuff from the Spell Compendium -- Bombardment, greater whirlwind, cometfall, Rapid-ized firestorms, arc of lightning, etc. If I was in bad trouble quickly, I'd toss out a Rapid-ized Nature's Ally VII or VIII, and run away as fast as my little longstrider-legs would carry me.
Clerics still have my money as "most powerful." A fully buffed cleric of Strength with his divine power, righteous might, etc. going would still wreck a battelfield...