I'm quite happy with "Any neutral", though I could live with some others. I couldn't live with "Any good", though; neutral evil druids are one of the great innovations of 3E.
In support of Nifft, though, I'd like to see a few more of the 511 possible alignment restrictions. (It's too late, unless a mod chose to get involved.)
I think NG is the most fitting alignment for a "normal" druid, because of their love for life (nature) and their strive for balance.
Twisted evil druids work well, too, kinda like the dark side of the force (of nature ) in Star Wars.
Nature is an expression of neutrality in D&D (and not only D&D), like all animals are neutral, etc. Therefore it makes sense for druids to be close to the center of the alignment diagram.
Well, why not allow for 3 classes for Druids. One for Good Druids called the True Druid class, one for morally Neutral Druids called the Grey Druids, and for Evil Druids called the Dark or Shadow Druids.
Well in my ideal world Law, Chaos, and possibly Neutrality(for sentients) would be removed and it would all be about Good (which is to say basic deccency on up...I dont jive with the DnD thing were you have to be a saint to be good, and an ordinary deccent person is "Neutral")
But in more likely to happen terms, I'd see all alignment restrictions on base classes removed.
I was very glad when the current druid alignment rules came into being though. You can finally have a druid who's a real person.