So, you want to try being a Balance Druid, eh?
First off, be aware that you will have a hard time getting gear. Blizzard just plain doesn't put much in there for you. As an example, there is literally ONE piece of leather caster gear in all of Karazhan, not counting the tier 4 tokens you can get and turn in for caster gear. One. I think there was something like 5 pieces of caster leather in heroics. So you face the dreaded decision:
To cloth, or not to cloth?
Ideally, I'd love it if Blizzard didn't all but force us to wear cloth. I'm managing to avoid it right now. But just doing the math, with the loot that's available right now, you're going to have to wear some cloth at some point in order to progress through endgame content.
Now, that being said, let's take a look at the foundation of any build: talents. This is my current build. I'm not going to say you must spec the way I did, but I'll explain the logic behind it. Also, please note this is presented as a "I'm level 70 and have a crapload of talent points to spend" situation. If you're leveling, don't follow this a "get X in Y order" type of thing.
Look at Fiord's Spec, or just look at the bottom of the page.
Starting off in the balance tree, you're going to want Starlight Wrath. You cast damage spells all the time, and those are your two non-instant damage spells. That means you're essentially taking .5 seconds off every cast. Duh. Nature's grasp is pretty much useless in PvE except to run away while you're outside. Useless for raiding.
Next, Focused Starlight and Improved Moonfire are must haves. As you'll see momentarily, crit % is very important to a Balance spec. This means your standard damage spells will be at +4% crit above what is listed in your character sheet, and moonfire will be at +10%. Verra nice. You'll have to take at least one point in Control of Nature to progress.
Next tier: Insect swarm, Nature's reach. Insect swarm because it's another DoT spell, and it reduces the chance that big nasty bosses are going to hit people by a little bit. Nature's reach because, well, it makes it more certain that you'll be far away from things that want to squish you. You have a choice here. You can either put some more points into Control of Nature, or pick up some Improved Thorns. I personally went with control of nature so that I could more reliably Cyclone something that is thwacking me and/or a healer. Improved thorns wouldn't be a bad choice either, help the tank keep aggro just a little bit more. It's personal preference there.
Next level, Take 5/5 Vengance first thing. A "normal" WoW spell critical does 150% damage, which means you're getting a 50% bonus to your damage. This doubles that bonus, so you get a total of 200% of normal damage on a crit. I also think that it is important to take Celestial focus. Not so much for the Starfire stun as the ability to mitigate casting interruption for one of your main damage spells. Sure, in a perfect situation, you're not going to be hit much. But if there are adds floating around, or the boss periodically hits everyone, or whatever, this helps you keep your casting flow smooth and uninterrupted. That being said, it's less important than some of the other talents on the balance tree, and is one of the areas where you might look to take points from if you feel you REALLY need X talent somewhere else.
Next level, again, fill 'er up. Everything on this tier is critical. Lunar guidance makes gear scale to a higher level automatically. What's not to love? Nature's grace speeds up cast times and helps you pour on the DPS faster, plus it's needed for the next ability up. Here's a dirty little secret I've noticed - the global cooldown is 1.5 seconds in general. So say Nature's Grace procs, and you get .5 seconds off your next Wrath, reducing it to a 1 second cast. Theoretically, you would finish the 1 second cast and still have .5 seconds left on the global cooldown before you could start casting again. This doesn't always happen. Whether it be the natural latency of the game (I generally run at a latency of ~100ms, for the record) or something else, I find that 2/3 times, I can start casting my next wrath right away. As for Moonglow, -9% mana cost to almost all of your staple spells. A mana saved is a mana earned.
Next tier up, Moonfury 5/5. It pretty much equates to +10% to your damage, period. 'Nuff said. As for Balance of Power: I tried raiding without it, and it makes a noticable difference. Your base chance to hit a raid boss level mob is 83%. This takes it up to 87%. What does that translate to? About 5% fewer resists, and thus about 5% more damage. Plus, the lessened chance of you getting nailed is better than a kick in the teeth. If you have a lot of +spell hit gear, you may want to pull points out of here. But the way I look at it, this lets me focus a bit more on spell crit gear and not have to worry quite so much about spell hit.
Up we go again, and you get your evil chicken of death form. It's quite nice to be a caster in low-plate level armor. Also, get Dreamstate 3/3. I cannot stress this enough. Dreamstate is a must have if you want any endurance in long fights as a Balance druid. Improved Faerie fire...the jury is still out. If your raid DPS is very physical heavy, it may be worth it to try to shuffle some points into here. If most of your DPS is done by casters, it's going to be all but useless. Potential things you could do are pull points out of Celestial Focus to put them here, or out of Balance of Power. Ultimately, it's up to you.
Next, not much choice here, but it's a good one anyway. Wrath of Cenarius 5/5. The thing to remember about this talent is that it scales in a nonlinear fashion. Example: You have a spell that does 1000 damage. You have +100 bonus damage. That means that this talent would increase the total damage of the spell by just under 1% (10 spell damage). Now, let's say that you get up to 1000 bonus damage. Now all of a sudden, you're increasing the total damage of the base spell by 5%. Much more respecatble.
Finally, Force of Nature. I personally like it - those trees may not hit for huge, but they're not wimps. Look at it this way: Each tree has a fairly quick attack speed - I've never seen exactly how quick, but I'm guessing around 2 seconds. Each hit does around 300 damage, and can crit. Even assuming they never crit, in 10 seconds that's 300 * 5 * 3 = 4500 damage over 10 seconds. If they last the full 30, that's around 13k damage. For less than 300 mana. Great deal.
Now, a quick detour over to the Resto tree.
First tier, get Improved Mark. There's no reason for Furor - if you ever need to go animal form, you should probably be ready for it anyway, at which point you can enrage for bear or just wait for cat.
Second, go for Naturalist. Nature's Focus would be my second choice, but I think that ALWAYS getting .5 seconds added to your cast time for Healing Touch will in the long run be worse than a chance to avoid spell interruption that may not always be there. Natural shapeshifter is generally a waste - shifting into and out of Moonkin is one of the less expensive shifts, and really, you should be needing to go to cat or bear frequently.
Finally, in the last level you're going to reach, grab Intensity and Subtlety. How much of each depends on your tanks, how you're doing with mana, etc. In general, Dreamstate is going to be more valuable to you than intensity will as far as mana regen in combat. That being said, it's never a bad thing to add in a bit more. I personally use 1 Intensity/3 Subtlety, as you can see. Find what works for you.
Finally, if you're using a build similar to this, remember a few things:
1) Intellect is your god. It not only gives you a mana pool and spell crit like normal, it also adds spell damage and mana/5. Load up on as much intellect as you possible can. Remember to take those numbers into effect when you compare gear.
2) Mana regen is your weakness. It's not as bad as it was pre-BC, but you're going to need to watch it. Ideally, you want to save your innervate for the healers of your group, so don't count on having it. Get a good cast sequence down, and follow it. If you need to, abuse the 5 second rule every now and then, but be aware that this will seriously cut into your DPS. Learn your mana needs - if you know you're going to need a potion at some point during the fight, don't wait until your mana is very low. Wait until the maximum effect of the potion would get you back to full, then drink. This starts the cooldown earlier, so if you end up needing a second potion, you're not waiting around doing nothing.
3) Spell crit is your friend. You have some key talents that come into play on crits - a lot of bonus damage ones which cascade through all your other bonus damage ones, a speed enhancement on your next cast, etc. Realize that because of this, casting more, lower damage spells can up your DPS. Basically, if you have an ability that procs on crits, you want as many crits as possible, which means as many hits as possible, period. If I crit 50 times during a boss fight, I saved 25 seconds of casting time. If I only crit 20 times, I only saved 10 seconds.
4) Moonkin is nice, but if you refuse to ever shift out of it and heal, you should've just rolled a mage. Remember, even in your normal damage gear, you're still a pretty damned good healer. In Kara, I normally don't do much DPS on the Valets - they hit hard enough that it's more valuable for me to keep all my HoTs up on the tank. There will still be enough DPS to take him down quickly, but there's much less risk that a lucky crushing blow or sequence of hits will take out the tank and leave the rest of us pretty much dead.
So, with sleep in my brain, I hereby close my first truly WoW related post here. Hope it shows you what you should be looking for in general.