I was just thinking along the lines of "aspects". You take "aspect of the predator", and you get +X STR, +X CON, +X DEX, and a melee attack that does X damage. You take "Aspect of the bird", and voila! You can fly! "Aspect of the Elemental" and you can set crap on fire, or let one of the wits in your group make some stupid pun (sorry, our druid is "stoned" right now... har har har). You could have a list of about six, seven aspects, all really easy to apply in play, and you'd be done.
I think it could also be cool if druids had a limited summon list, so they could only summon a few different types of creatures, that improve as the druid casts higher-level summoning spells. If the druid player only had two summoning options, odds would be better he'd already have them statted up, right? To compensate for the weakening of versatility, put some bonus on them (they all have a minor aspect of the elemental! Flaming Birds! An Airy Flock of Seagulls!)