Well, I am generally for sticking close to the SRD, at least somewhat. More because no one has ever done that before. Even if you just use options from the SRD in ways they aren't supposed to go together, or renaming them or stuff. Or even daisy changing alternative class features. Heck, I love thug sneak attack fighter and feat rogue -- when you multiclass between them, you make a great swashbuckler, if you do it right!
Like take this:
http://www.d20srd.org/srd/variant/classes/classFeatureVariants.htm#rageVariantWhirlingFrenzyThat's my favorite rage variant. Perhaps you could give the Barbarian that (it's better than Rage) and the Druid Rage in the way those options mention? So one is strength and attack based (remember it works on a charge or a standard action!), one is more Strength and Constitution based? If only to differentiate them?
I mean, I'd personally give the Barbarian AND the Druid Pounce (at least when they could get it normally; 1 for barbarian, 5 for druid with wild shape), but that's just me. Pounce just makes combat soooo much more dynamic and mobile!
Heck for monk, I especially like the Passive Way variant of the Monk... but generally only if Improved Trip gives some of the bonuses that you are saying it won't. (sad...)
And I don't like natural armor overly much. It's okay, I suppose -- but things like miss chance are wayyyyy more important than armor in D&D. And it's not like this Druid can make their natural armor an insight bonus to ac to apply it to touch ac, like a sorcerer or wizard can.
Remember, Druids can wear Leather, Studded Leather as long as the studding is alchemical wood, various types of Chitin armor (of which there are light, medium, AND heavy), Hide Armor, various types of Ironwood Armor (breastplate most commonly, sometimes also banded mail, rarely full plate), dragonhide full plate, etc. etc. Go out of core and there are woods that act similarly to Mithral. AND they get a spell combo that makes essentially infinite masterwork Ironwood breastplates that they can temporarily make +1 breastplates, by level 12 or so. So they won't usually be lacking armor.