[Aerich]

Faster level progression as a druid. A druid 7 will have the same XP as a druid6/monk1.

If you aren't going to get the shapeshift mod, I'd pick a level (or 4) of fighter over monk levels or barbarian levels. A bit of extra AC while shapeshifted doesn't help all that much (a lot of the shapes are kind of weak for the level at which you achieve them), but the movement bonus is ok. I'm not big on Rage, either, since it wears off and becomes a liability (because of the subsequent fatigue) in a fight of any consequence. Again the movement is ok, as is the bit of extra HP.

If you really want a mix-in class, how about fighter? It won't hurt your BAB, it'll give you an extra feat (GSF: Evocation and Transmutation are good for druids, as are Spirit of Flame and Scion of Storms), and allow to use whatever weapons and armour you want. You can make your druid a very good melee attacker with 4 levels of fighter and specialization if you wish (recommended 18 Str and specialization in a two-handed weapon proficiency like Polearms). Save most or all of the fighter levels until after you hit 20 lvls of druid, though.