Druids are undoubtedly one of the most powerful and versatile core classes, but also a very confusing one, especially for newer players, because of the variety of options they have. This guide is meant to point out key elements you can pick up during your career, so that you can enjoy the game with minimal book-keeping, while still being able to face pretty much everything that gets thrown at you.
This is pretty straightforward. You need two things: constitution and wisdom. Unfortunately races that give bonuses to those attributes are quite rare. The following are the best druid races, according to the books you are using:
Human: Probably the best pick even in a non-core environment. That extra feat is what makes the difference. Druids are not feat starved, but it helps getting more powerful abilities at earlier levels.
Dwarfs: Not much, but it's an ok choice. Stability and constitution bonus along with darkvision and some nice racial bonuses.
Forest Gnome: Better than the normal gnomes and dwarves due to their innate ability to use the pass without trace spell at will. Also three automatic languages and a very basic that allows them to communicate with forest animals, which fits a lot more thematically with druids.
Free For All:
Anthropomorphic Bat SS: Huge bonus to wisdom and blindsense. You can apply the dragonborn template-like race if you want a bonus on constitution, too.
Dragonborn Buomman PlH: The first race to provide bonuses to both wisdom and constitution! The drawbacks are not important. Note that the racial vow of silence buommans have is waived due to the dragonborn transformation.
Dragonborn Desert Half-orc UA/RotD: A +4 bonus to constitution with penalties to intelligence and dexterity. It's the best half-orc race around for druids. It is mentioned because of the awesome half-orc druid substitution levels.
Venerable Dragonwrought Jungle Kobold UA/RotD: Jungle because it's the only one without a hit to constitution. You end up with -4 str +2 dex +1 int +3 wis +3 cha.
Dragonborn Lesser Aasimar PGtF/RotD: -2 dex +2 con +2 wis +2 cha.
Halfling PGtF: Namely, the ghostwise and strongheart varieties from the Player's Guide to Faerun sourcebook. Ghostwise halflings can communicate telepathically, which will enable communication with your team members, without the need to invest in items or other abilities. Strongheart halflings receive an extra feat, just like humans. The main benefit here is that they are able to choose the Yondala's sense feat (which is like improved initiative, but a lot better, since you get your wisdom modifier as a bonus instead) and the halfling alternative class levels.
Concentration: Because you'll probably be casting in melee after you get wild shape, you need to max it out. Even if you use wild shape forms as a defensive form for casting (such as a high AC flying form), i'd still wouldn't pass on this.
Craft: Unless you want to fulfill a certain requirement, i wouldn't get this. This skill however, has some use. To create a bogun with the beget bogun spell, you need to make a craft (basketweaving or weaving - i don't even have to say which is better) 12 check. I love those little critters, so i'd probably get 2 ranks in the legendary craft (basketweaving) skill and take 10.
Diplomacy: With this you can even be the party's face if need be. You can also use it to haggle and get a discount on items.
Handle Animal: Important due to the synergy with animals and your animal companion. You need a total score of +20 to make the most of this skill, which means that you need to spend ten ranks more or less (assuming you use take 10). I'd get it to 5 ranks if i needed the wild empathy synergy bonus. Check the handle animal guide for more information.
Heal: Not much here. If you feel like it, you can spend 5 ranks and take 10 to use some of the skill's functions.
Knowledge (Nature): It's your only knowledge, so it would be best to max it. It's quite important and gives information for many creature types.
Listen: Spend at least 12 ranks in this skill to make use of the listening lorecall spell.
Profession: Nah, i'll pass.
Ride: Only useful if you want to use your animal companion as a mount. Still, only a few ranks are needed.
Spellcraft: This depends entirely on the campaign. If you have another spellcaster in your team that is able to identify spells, just spend one rank on this. Otherwise it's a good idea to max it. If you are going to play in an epic campaign, max it, as you'll need it for epic spellcasting.
Spot: This usually comes with listen. Spend a few points if you feel like it or your party is in need of a scout.
Survival: Get it to 5 ranks for the synergy bonus. You can max it out, it's a skill with druidic feel. You can get the track feat to benefit most from it.
Cross Class Skills:
Use Magic Device: If you have ranks to spare, invest just one here.
Autohypnosis: This is great! It has wisdom synergy and a synergy bonus from concentration, so you can get it at high levels without investing many ranks. It has cute functions, too.
Listen to This: Useful if you are going to be the party's scout.
Swift Concentration: Druids have many duration: concentration spells to make this wonderful skill trick useful enough to get.
The feats druids need can be broken down to three categories: summoning, casting and wild shaping. The newest druid's handbook has detailed information about all of them. I'll just note here the most important feats:
Augment Summoning: +4 bonus to strength and constitution is a good bonus, but the problem is that it requires a useless feat, spell focus (conjuration). Luckily for us, there are ways around that (like initiate of malar or the 7th half-orc substitution level). The strength bonus will almost always provide your summons a better chance to hit and more damage. The constitution bonus will give them more hit points and make them even tougher. Remember to adjust any special abilities (for example: trample and many special attacks from elementals).
Natural Spell: This feat is so good, all druids should get it. When playing a druid, just remember to take this no matter what at 6th level. It is often said that this is not a feat; rather it's a class feature the druid gets at 6th level instead of a bonus feat.
Greenbound Summoning: Very powerful feat, especially at low levels. It's so good, it's cheesy. Most DMs will ban this outright. Since if you get this you'll want to summon animals mainly, you can skip augment summoning and get it through initiate of malar or the half-orc druid substitution level, as those only affect animals.
Dragon Wild Shape: Another great feat, a must have at level 12. You get all supernatural and extraordinary abilities of the dragon you wild shape into. Note that dragons normally speak and can cast spells, so you probably don't need natural spell, but i need input in this one. Dragon forms are perfect for defense and they enhance your senses: don't forget that all dragons have darkvision 120ft, blindsense 60ft and immunities to sleep and paralysis. Additionally, they often have large amounts of natural armor (somewhere around 10 at small and medium size), which you can further enhance with barkskin. Some great forms (from Draconomicon mainly) are Shadow, Battle, Ethereal and Oceanus dragons. Last, but not least, dragons are able to use items, so you can just take them off and re-equip them after wild-shaping.
Initiate of Nature: This feat allows you to rebuke animals and plants. You have the ability to control 1HD per class level, which results in quite a few creatures. Combined with the animal buffing spells you receive, it's like creating a personal army. You can check out some of the dire animals for worthy candidates. Generally, if you summon a creature that you like often, it's a good idea to rebuke it.
Quicken Spell: Summoning is usually a full-round action. At later levels, using quicken spell will enable you to drop some low level buff or battlefield control spell, like entangle, while summoning.
Minor Shapeshift: Nice if you have nothing to fill your 9th level slot with. You can power it with baleful polymorph, which is a useful spell anyway. The most useful modes are Vigor (which gives you temporary hit points equal to your hit dice - you can replenish them every round) and Might (+2 on melee damage rolls, awesome with a fightning wild shape form). It's also a very good pick for a front-liner druid.
Level-0: Not much here. Detect Magic, Light, Know Direction.
Level 1st: Entangle (a must!), Obscuring Mist, Endure Elements, Omen of Peril SC, Beastland Ferocity SC.
Level 2nd: Blinding Spittle SC, Gust of Wind, Barkskin, Snake's Swiftness (mass) SC, Kelpstrand SC.
Level 3rd: Primal Insticts DrM (+5 initiative for 24 hours!), Grater Magic Fang, Alter Fortune PHB II.
Level 4th: Boreal Wind Frost, Blast of Sand Sand, Enhance Wild Shape SC, Greater Luminous Armor BoED, Last Breath SC.
Level 5th: Owl's Insight SC, Baleful Polymorph, Animal Growth, Quickened Entangle.
Level 6th: Bite of the Werebear SC, Superior Resistance SC, Antilife Shell, Energy Immunity SC, Spellstaff.
Level 7th: Master Earth SC, Word of Balance SC.
Level 8th: Frostfell Frost, Word of Recall.
Level 9th: Summon Elemental Monolith SC, Nature's Avatar SC, Foresight.
Ring of the Beast CC: Pretty affordable ring that will upgrade your summon nature's ally spells to the next level, assuming you have access to it. Very useful and part of a three-item set which work while you're wild shaped. I eventually get them all (swift action wild shape, +1 wild shape per day and +1 level for wild shape are the highlights), but unfortunately they're pretty expensive.
Periaph of Wisdom +X: Standard issue.
Metamagic Rod (Extend, Lesser): For extending your low level buffs, pretty affordable. Also, creeping cold.
Monk's Belt: Standard issue. You may need a wielding clasp to go with it, unless your wild shape form can use items without help.
Bead of Karma: Expensive, but will increase your caster level for your buffing period for a good amount.
Ring of Mighty Summons CM: Cut the summoning time in half, but the hit points of any creature you summon with the next summoning spell has maximum hit points per hit die. You can couple it with the Ashbound feat. It functions three times per day and it's somewhat pricey.