Now, I know what you all are thinking: "*groan* not another person making self-interested posts trying to make their favorite class better."
Weapon enhancements. (okay, I lied, this one I admit would make druids more powerful) Everyone who can cast a spells gets some form of them, except druids. GMW seems a little over-powered, as does flameblade/darkfire - on the other hand, Clerics get both, so one or the other might not be too overpowering. The ranger's blade thirst might be a good candidate for a druid spell, with the whole redistributing primal forces, balanced healing as you harm kinda thing, except the slashing/piercing requirement would leave a lot of druids out in the cold, (yes, there are druids who don't use scimitars exclusively). Of all the weapon enchantments, however, bless weapon seems the most thematically appropriate to druids - ending the scourge of undead and aberrant creatures and all that. Since it's a level one paladin spell, level three druid spell would be a relatively close approximation - but, if people feel that's too powerful, make it a level four or five spell instead.
Speaking of undead... Druids really aren't that good at it. In Layo, clerics are not really about harming undead (necessarily), but still have all the anti-undead mojo. Druids, on the other hand, while very diverse, often take up that mantle of going after undead, as they harm the balance. People are always surprised when I tell them the spells that Pallena can't cast. Other than cure/heal, druids get two very nice high-level anti-undead spells, sunbeam and sunburst.. and that's it. And they're at the same spell level, so its difficult to really have an undead arsenal. So, one possible solution would be to move one of the spells a slot higher or lower. Another would be to give druids something like undeath to death (which even wizards get), at level six or seven. Searing light might also be a nice addition for low level characters.
Defensively, druids also suffer at the hands of undead. Druids get death ward, which is nice, but again, that's all. Undeath's eternal foe and Shadow shield would be thematically appropriate, but as they are the singe best group and individual defensive spells in the game, they might be a bit unbalancing. Negative energy protection seems to me to be an appropriate spell to give to druids - again, if its viewed as being unbalancing, kick it up to level five or six druid spell, or something along those lines.
On high level spells more generally: Druids get two special druid spells at high levels: Nature's Flow, and Nature's Balance. Both have nice druidy names and descriptions... but are rather useless. The big problem with nature's flow is the DR that it gives you. When nature's flow is cast, it overwrites the DR from stoneskin or similar spells (and Pallena at least lives and dies with her greater stoneskin), and leaves you defenseless when it expires. Maybe the DR could be changed to an AC increase or to concealment instead? Nature's Balance... I don't think I've even ever seen the spell cast. I can think of some situations where it might be useful, but the downsides seem pretty large for a level nine spell - compare to implosion, for instance - both affect up to four enemies... but implosion doesn't have the severe downsides. Its rather unfortunate, but Storm of Vengeance so outstrips the other ninth level spells, there really isn't very much reason to memorize anything else... and so the spells loses its awe and cool druidy storm factor. Having another spell or two with comparable oomph would help.
A while ago there were discussion about changing the Shapechange spell to have some other forms for various reasons (see here). I have no idea whether this is something that could easily be implemented... but its sure would be nice to have something that reflects nature more. Shapechange sure sounds like a great druid spell, but right now the red dragon form is really the only thing that seems vaguely druidy - I mean, why on earth would a druid want to shift into an iron golem? As far as I'm concerned, the stats could stay the same, but if the shapes could be changed to, say, griffons, or ancient dire wolverines, or the Voltrexian penguin of doom It would really turn the spell into something that could have some RP use.
I'm not opposed to a mage who has the power to turn into a demon, dragon or golem actually being able to kill something in those forms. If during the mage duel of Sword & the Stone, Merlin turned into the dragon and declared "oh ho! I am now a sitting duck with limited battle potential who can't cast spells, kill me in two rounds!" it would have been rather anti-climactic.
Finally... Again, no idea if this is even possible, but it would be really really really nice if the animal empathy skill could be used on critters like snakes and spiders and giant bugs. It just seems weird that a druid can tell a gargoyle to behave, but not a snake. And its incredibly frustrating to preach the virtues of all natural creatures, and how you shouldn't step on the spiders, only to have one attack you and be forced to kill it or die yourself. I would love it even more if druids could walk through nature-friendly things like treants or satyrs without incurring their wrath, but that might be too much of an advantage.