A newer version of this part can be found at: Wotlk Paladin Tanking Guide part 2: Talents (Patch 3.1)
How should I pick my talents?
I will comment on each talent from the protection tree, plus the relevant talents from the retribution and holy tree. Additionally I will give each talent a score from the following coloring system, from best to worst:
MustHave - Epic talents that every paladin tank should have.
GoodToHave - Talents very good to have and will help your tanking a lot.
TakeOrLeave - Talents that will help your tanking, but not at all mandatory.
LeaveIt - Useless talents when it comes to tanking.
Note that the scores are given based on my personal experience and opinion only.
Blessing of Kings and Improved Blessing of Kings
The 2nd best tanking blessing, many tanks even consider BoK as the best blessing, because 10% stats is a huge deal!
Now that paladins also receive block value from strength, Divine Strength has become a very good tanking talent, that is probably why it was moved from the holy tree. The extra threat is just a bonus.
PvP talent, the benefits are almost useless to tanks.
PvP talent, totally useless.
Mandatory tanking talent and the only one worth taking in the whole tier.
Improved Righteous Fury
Tanking is about two things, threat generation and damage mitigation. This talent provides 6% damage reduction, there is no need to say more.
Tanks always want to have more armor, the reduction to movement slowing effects is a bit useless though, due to Hand of Freedom.
I have seen many tanks spending points in Divine Guardian, but I must admit that I am not a fan of this talent. As a tank, you almost never use your bubble, except in macros for removing debuffs, in which case it is removed immediately. It is handy when you are not tanking though, Divine Guardian can be used as a mini Shield Wall for the whole party/raid.
Improved Hammer of Justice
I have only seen a very few tanks spending points in Imp HoJ, but this talent is very useful in my opinion. HoJ is our only way (unless you are a bloodelf) to interrupt spells, with this talent, we can use HoJ twice as much as before.
Improved Devotion Aura
As I mentioned before, tanks always want to have more armor. But it is the bonus healing effect that makes this talent truly incredible. 6% addition to the amount healed may just be the 6% that saves your ass, you will love this talent, your healers will love this talent, even the damage dealers will love this talent.
Blessing of Sanctuary
Damage mitigation and threat generation in one talent, this is the best blessing a tank can have, unless you are a bit undergeared for the encounter, in which case BoK will benefit you more.
A very popular talent due to the fact that it roughly doubles your damage output for the duration of the proc. When fighting multiple mobs, it procs all the time, which makes Reckoning one of our best grinding tools. But is it good for tanking? The extra threat from the proc is great, but I still consider Reckoning a bad tanking talent, because the proc makes you hit more. The more you hit the more you get parried, the more you get parried the more damage you take. When tanking hard hitting bosses, this talent can be your death.
(from this point on, the talents are more or less mandatory, most tanks will maximize the rest of the protection tree)
Tanks always want to have more stamina, even more than armor! The bonus effect to bubble is useless for the same reason as in Divine Guardian.
One-Handed Weapon Specialization
Another great tool to help you generate threat.
Damage mitigation, the chance to mitigate damage and threat generation in one talent, this is the best talent I have ever seen! Keep Holy Shield up at all times! And yes, I have given Holy Shield the legendary color, because it is that good:)
This talent is is underestimated by many, sure it wont save you from hard hitting bosses like Brutallus, but it increases your effective health by a great amount. There is an addon to register how many times Ardent Defender saves you from dying (I can't remember the name, sry), I was surprised to see the number, because I myself was one of those who underestimated this talent, I don't anymore.
Again a super talent, more block value equals more effective health and more threat. The increased chance to block is a useful (useless you already are block-capped) but unreliable bonus.
Tanks always want to have more stamina, they also want to have more expertise, because expertise reduces the chance that you will get dodged and more importantly parried. The additional crit chance is nice too.
Touched by the Light
The damage (thus threat) a paladin deals is based on attack power and spell power, spell power increased by 30% of your stamina is a huge amount, because as a tank, you will have high stamina. I don't know why it comes with a healing bonus though, it is useless to tanks since we almost never heal.
This is the ability I use most of the time when pulling mobs, generates a great amount of threat initially. Combined with Exorcism and Judgement, the threat paladin tanks generates in a pull makes all other tanks cry for their mother.
Guarded by the Light
6% less spell damage taken is very nice. And so is the mana cost reduction, it helps you handle overgeared encounter where mana can be a problem.
Shield of the Templar
The amount of threat generated from Holy Shield and Avenger's Shield is not that high, but Shield of Righteousness is your highest damage and threat ability, that is why 30% more damage from those 3 abilities is insanely high. My Shield of Righteousness often crits for 7-8K.
Judgement of the Just
One of the first things I learned when I was a warrior tank, was that I have to keep Thunder Clap up. Well, this is our Thunder Clap, and it comes with Judgements, which we will be using anyway.
Hammer of the Righteous
This talent is what keeps us on the throne of the best AOE tanking class! What makes it even better is in addition to the "3 times your main hand damage", it also applies the active seal to all 3 targets.
Inspite of being in the retribution tree, this is a tanking talent, and a very good one.
Since all the abilities we use when tanking are instant abilities, this talent is helpful for keeping the mana up, but imo far from worth investing 5 talent points in.
A must have for paladin tanks due to the 96969 rotation (I will come back to that later), but only 1 point, not 2!
Heart of the Crusader
Very useful talent in encounters with a time limit, or in general to speed up the killing process. But every retribution paladin and most holy paladins have this talent, so it's not a must have for tankadins.
Persuit of Justice
Used to be a very popular talent among prot paladins due to the fact that it used to reduce the chance of you being hit by spells. Sadly not anymore. The speed bonus is still very nice though.
Seals of the Pure
Since you will be using either Seal of Righteousness or Seal of Corruption/Vengeance when tanking, this is a very good talent for additional threat.
This is my "basic" build, where I have left out 7 talent points, I usually put 3 points in Imp HoJ and 3 points in Heart of the Crusader, because I never have problems with threat. If you are not comfortable with your threat generation, you may want to put some points in Seals of the Pure.
A note on Blessing of Kings, most holy paladins nowadays have 18 points in the retribution tree for gaining 8% crit chance on their heals, which makes BoK unaffordable to them. In case you don't have a retribution paladin with BoK in your party/raid either, you will miss this incredible buff, that's why I always have BoK.
Part 3 is about glyphs and maybe enchants, to be continued...