The true final boss of Cataclysm's first tier is a hotly debated topic. With three different raid instances available at launch, the end boss in each raid zone could be eligible for the top spot. While most people will agree that Al'Akir is only a secondary opponent, Nefarian and Cho'gall are both old and powerful enemies. Cho'gall has been covered in the WoW comic books with great detail, while Nefarian is so common in WoW that we've already killed him once. Sinestra could even make her claim for the throne, as she is a difficult, heroic-only boss.
In my opinion, Nefarian is the final boss of tier 11. He's Deathwing's son, which makes him public enemy #2. During the encounter, we're faced with not one but two dragons, plus all the doomfire and adds that we can handle. The Nefarian encounter is the type of fight that I would've hated before Cataclysm. Now, we have AoE abilities to handle the incredible raid damage and the mana management tools to keep ourselves from running dry.
Mana conservation is key
Every phase of the Nefarian fight is going to require more healing than the last, and so maintaining your mana levels throughout the encounter is your main focus. We'll be taking every precaution and cheating our mana pool every way we can. Nefarian is the longest fight of the tier, and so you'll need to save your mana early so that you've have it available in the late game. I've heard so many stories of guilds wiping to Nefarian in the low percents because their healers finally ran out of mana.
Phase 1: A clean transition
In the fight's early moments, there's not going to be a lot of healing needed. Only the tank facing Onyxia should be taking much damage, and that's easy to heal through. As Nefarian starts summoning his skeleton adds, you can assist in rounding them up. I use my Hand of Reckoning, Righteous Defense, and Holy Wrath abilities to help our ranged DPS control them and get them into position. I would consult your raid leader for instructions here, as you may be needed to heal elsewhere.
Once Nefarian lands, both tanks will be taking damage, but again, this isn't very hard to handle. You should exploit Holy Shock and Word of Glory as often as you can, using the two-heal method to stretch your mana to its limit. Try to avoid Divine Light if you can, as Holy Light is more efficient. If you're below 90% mana at this point, try to remove any excess Divine Lights and use Judgement more often. If you're Judging on cooldown and abusing Holy Shock and Word of Glory, you can get by without spending much mana at all. Provided that everything goes right, you'll have nearly 100% mana once the first Electrocute occurs.
Holy Radiance is the perfect counter to Nefarian's powerful Electrocute/Crackle ability. Electrocute deals significant nature damage to the entire raid, so Aura Mastery is useless against it. Holy Radiance, on the other hand, can heal for insane amounts since your group should be stacked up pretty tightly. Use HR immediately after each Electrocute, and you'll see your raid frames return to green in no time. Coordinate with your raid to use Divine Favor and Holy Radiance on one of the Electrocutes that someone isn't mitigating with another cooldown like Divine Guardian.
The raid doesn't really take much damage between Electrocutes, and so you should only use Holy Light to finish topping everyone off. This phase is the perfect example of the new healing paradigm: Nobody is in danger, and so you can safely use your cheap, slow heal.
You don't have to eat all of the damage in the phase if you're clever with your cooldowns. I use my glyphed Divine Protection for every single Electrocute, which significantly reduces my chance of dying and the amount of healing I need to do. In addition, I toss Hand of Sacrifice on my tank a couple of times during phase 1, absorbing some of the melee and fire breath damage he's taking. Protector of the Innocent and Enlightened Judgements will take care of the incoming damage, so just spam Holy Light on the tank and enjoy all of that mana you're saving. You'll probably have to use a couple Divine Lights on the tank, since your globals are being used to heal the raid, but that's okay. You want to use every trick in the book to minimize your incoming damage and maximize your outgoing healing. You're going to need every point of mana you can scrape together for phase 2.
Phase 2: A test of patience
I personally use my Divine Shield to nullify any stacks of the nasty Magma debuff I acquire while making my way up to my assigned platform. Try to toss out Holy Shocks and Words of Glory as Onyxia is dying, as you'll want your group topped off. As soon as Onyxia perishes, I pop my Divine Plea and run to get into position. Nefarian's deadly Shadowflame Barrage is going to be assaulting you for the next few minutes, and you need to be mentally prepared to handle it.
It's completely possible to heal your platform (on 10-man difficulty, at least) with only Holy Light, Holy Shock, and Word of Glory. While you're going to see massive amounts of incoming damage, it's not entirely untenable. You can resist the shadow damage, and as long as you're constantly healing, you can prevent yourself from getting too far behind. Resist the urge to use Divine Light, as it's usually not necessary. If you abuse the two-heal method and simply continue to spam Holy Light, Holy Shock, and Word of Glory, you can keep everyone alive without taxing your mana too greatly. Aura Mastery is a lifesaver here, as it can give you a few moments to catch your breath. I typically use AM immediately after phase 2 starts to get everyone stabilized.
You need to be confident in your healing capabilities in order to make it through phase 2 successfully. While seeing your group's life dip into the red may be scary, you can work your way through it. Continue to heal, toss Beacon of Light on someone on your platform, and simply ride your cheap heals all the way home. If you find yourself leaning on Divine Light in this phase, you're going to be hopelessly out of mana when phase 3 begins. You have to learn how to heal with only our cheaper heals.
The only time you need to use a bigger heal is when Electrocute is coming, and I again suggest Holy Radiance. Your Divine Protection plus Holy Radiance should be more than enough to keep your platform alive through the burst. I will use a couple of Divine Lights just to ensure everyone under my watch is at 100% life going into the Electrocute.
Phase 3: Raid healing
Depending on your guild's exact strategy, you're going to be dealing with about six Electrocutes in phase 3. That's a ton of healing that needs to be done, and so you'll be using every trick in your book to get it done in time. You'll likely be under the effects of Bloodlust during this phase, so try to get two full Holy Radiances in under the haste buff. I follow that up by using Divine Favor and Avenging Wrath on two more Holy Radiances, which ensures that each of them is as effective as possible.
Your tanks will still be taking reasonable damage, and so you'll need to figure out who's assigned to healing who. Because Holy Radiance only costs us a single GCD and a bit of mana, you should be using it right after every Electrocute, regardless of your assignment. Don't hesitate to use Divine Plea after everyone's stabilized and you're awaiting your next Electrocute. I was able to find a 9-second window right after Bloodlust where everyone was topped off and I was able to regenerate a ton of mana.
Because you can't exactly stop Electrocute, you might need to pull out your big heals. If someone is at 40% and an Electrocute is imminent, use Divine Light or Flash of Light to bring them up quickly. The secret is to minimize the amount of Divine Lights you need to use in order to preserve your mana. You've been saving your mana for this moment, so don't hesitate to use a big heal, since it could cost someone their life. Continue to hit your tank with Hand of Sacrifice to reduce his incoming damage. You should be able to use Divine Protection on at least half of the Electrocutes, making the glyph a no-brainer for this fight.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Learn the ropes in Cataclysm 101 for holy paladins, study the new balance between intellect and spirit and learn how to level your new Sunwalker. Tanking is a job, DPS is a craft -- but healing is truly an art.