From the WOTC Optimization Board:
Druids are the defenders of nature. They have mighty divine spells in their repertoire, call powerful companions on their side and wildshape themselves into strong forms to join combat.
A) Q&A:
Q: What is the Druids major strength?
A: There are several. Divine casting is the major power, but wildshape as well as their animal companion can be very powerful as well.
Q: What is the Druids major weakness?
A: A Druid normally suffers from a low AC because of his limited proficiencies and the missing ability to carry armor while wildshaped. With only medium BAB and HD Druids should avoid the frontline until they have powerful wildshape-forms and buff-spells in their repertoire.
Q: What are the most common Min/Max mistakes for this class?
A: I would say multiclassing is a serious error in many builds. Druids are best taken straight unless you want to focus on a special aspect, in most cases you lose all the others then so its a hard descision.
Q: What are good Break-Offs when using the Druid in a multiclass build?
A: Druids have a well balanced list of features so its hard to say. If you need many levels for a PrC Druid 8th is a good point, you get wildshape (Large) which covers many things.
If you just want a few levels Druid 15 or 16 is a breakpoint with wildshape(huge) resp. wildshape(elemental)
B) Techniques:
I. Sources
a. Most Important Source is still Masters of the Wild
b. Other Sources are Complete Warrior with Natures Warrior and Warshaper, Book of Vile Darkness with the Vermin Lord, Book of exalted Deeds with the Lion of Talisid Unapproachable East with the Talontar Blightlord, the Players Guide to Faerun with the Divine Disciple and Defenders of the Faith with the Hospitaler and the Contemplative.
II. Ability Scores
a. Overview
Druids need Wisdom for spellcasting. Con is important for hitpoints
(short note: its still under debate if hitpoints change while in wildshape, this text assumes that it is not the case)
i. Strength is a dumpstat, just look out for your carrying maximum. Wildshape takes care about it otherwise.
ii. Dexterity is altered by wildshape anyway so all you need is to survive until then.
iii. Constitution is an important attribute for any character. If you plan to make up a frontlining Druid you should put your points here.
iv. Intelligence is not that important. Druids have 13 classskills, decide yourself how many above 4 you need to have maxed.
v. Wisdom is prime for spellcasting.
vi. Charisma is normally a dump-stat.
III. Race
Humans and their extra feat and skillpoint are always a good choice for a Druid.
Gnomes make up great Druids due to their good ability-adjustments. With wildshape being independant from size being small helps a Druid.
IV. Skills
Knowledge(nature) and spellcraft are the two primary skills, complemented by concentration, survival and spot.
V. Feats
Natural spell is the feat of choice for almost any Druid.
Spellfocus(conjuration) and Augment Summoning strengthen the summoning-skills,
Rashemi Elemental Summoning (Unapproachable East) adds a template to summoned elementals.
Vow of Poverty adds nice possibilities for a Druid while Exalted Wildshape and Exalted Companion power the good Druids. (all BoED)
Dragon Wildshape (draconomicon) is an interesting feat as well.
VI. Deity
As long as you dont plan to pick up a PrC like Divine Disciple or Contemplative the choice of a god is not influencing your power.
VII. Builds
See:
http://boards1.wizards.com/showthread.php?s=&threadid=81471
See also:
http://boards1.wizards.com/showthread.php?p=6718617
http://boards1.wizards.com/showthread.php?t=290658