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RETRIBUTION
Retribution paladins are the DPS build for the class. It is important to note that while Retribution paladins don't have the DPS output of man melee classes nor the multi-mob damage of Arms warriors, their contribution is not solely DPS. With a wide variety of buffs, auras, spot healing, and the wipe-evasion of Lay on Hands, Blessing of Protection, or self-sacrifice. Against a single target, a properly geared Retribution paladin can match or surpass a similarly geared Arms warrior.
Talent Build
My talent build (http://wowhead.com/?talent=sxx0MZZVfcthcuiIot) does not follow the classic classic 5/8/48 build (http://www.wowhead.com/?talent=sxZxhZEf0t0cuiIot).
This is designed for a mix of DPS and survivability for both PVP and PVE, and differs from many "stock" retribution builds you will see online.
On the Retribution tree:
Benediction is to lower the mana cost of Judgements and Seals as Retribution paladins go through mana very quickly. Spiritual attunement (http://www.wowwiki.com/Spiritual_Attunement) does not come into play as it would for a Protection paladin so every bit of mana efficiency helps.
Improved Judgement decreases the cooldown of your Judgements - and as a Retribution paladin, you should be spamming judgements as much as possible.
Improved Seal of the Crusader - judge Crusader on an opponent, and all attacks have a 3% increased chance of critical strike. Yes, please.
Vindication gives the Paladin's damaging melee attacks a chance to reduce the target's attributes by 10% (15% next level) for 15 seconds. While this is not as useful in PVE as many bosses are immune, it is very useful in PVP.
Conviction increases critical strike chance by 5%.
Seal of Command (http://www.wowwiki.com/Seal_of_Command) is the bread and butter for Retribution paladins. In order for this to be used effectively, it is imperative that the paladin use a slow weapon to ensure the Seal procs more often. Follow a Hammer of Justice with a Judgement of Command, and you do double damage. Note that while in PVE, Seal of Blood (http://www.wowwiki.com/Seal_of_Blood) is better for Blood Elf paladins, in PVP it is generally not considered wise to use a seal that trickles your health down.
Pursuit of Justice reduces the chance you'll be hit by spells by 3% and increases movement and mounted movement speed by 15%. This is very useful in PVE to ensure you can keep up with a runner. In PVP, couple this with a Judgement of Justice - which at rank 2 works to ensure players can only move at their normal run speed, whether mounted, sprinted, or in travel form - and you can overtake any opponent.
Crusade was taken for increased 3% damage against humanoids in PVE and PVP; demons, undead, and elementals in PVE.
Two Handed Weapon Specialization increases damage by 6% with two handed weapons. This is a must-have.
Sanctity Aura increases all holy damage against your target by 10% - a Retribution paladin should have this aura up all the time. In addition, the Improved Sanctity Aura increases all damage by 2%. This is great for PVE parties.
Vengeance not only looks cool when it procs, but it also gives you a 5% bonus to Physical and Holy damage you deal for 30 sec after dealing a critical strike. It also stacks up to 3 times. Yes, please.
Sanctified Judgement returns 80% of the mana from a judgement. As stated above, Retribution paladins should be judging whenever the cooldown is up, and their mana pool is tight.
While Sanctified Seals increases your critical strike chance by 3%, the more important feature is the 100% reduction that your seal will be dispelled. This is very useful in PVP/
Repentance is a CC against humanoids that lasts for 6 seconds. Somewhat useful in PVE, very useful in PVP.
Fanaticism reduces all threat by 30%, which is essential in PVE. It also increases the critical strike chance of Judgements by 15%. So, Hammer of Justice, Judgement of Command. Huge burst damage when you crit.
Crusader Strike is the only instant strike talent this melee class has, doing 110% weapon damage. Just as importantly, it refreshes all judgements on the target. Couple this with a Protection paladin tanking and you have superb synergy.
Reasons for ones not taken in the Retribution tree:
Improved Blessing of Might - looks very promising, but the 5 point cost here is better places into Divine Strength. For the first tier, Benediction is far more important, as a paladin can not operate without mana.
Deflection is a nice choice for Protection paladins, but not as critical for Retribution paladins.
Eye for an Eye looks very sexy - reflect damage on a crit back on the spellcaster? However, if you crunch the numbers, you'll find that to be effective would require that the paladin be struck with such an amazingly large critical spell hit that he is good as dead anyhow.
Improved Retribution Aura is a no-no. A Retribution paladin should never have this aura active!
Divine Purpose lowers damage from melee and ranged critical strikes. Nice, but I chose to spend the 3 points elsewhere.
On the Holy tree:
Divine Strength increases total Strength by 10%. Strength translates directly to Attack Power.
Spiritual Focus gives your Flash of Light and Holy Light spells a 70% chance to not lose casting time when you take damage. This is one of the non-typical choices. Being able to heal while players or mobs are beating on you is, in my opinion, quite useful.
Unyielding Faith increases your chance to resist Fear and Disorient effects by an additional 10%. One of the issues a Retribution paladin faces in PVP is being fear chained. Since paladins do not have any ranged attack (save Hammer of Wrath) it is critical that they stay within melee range.
Arguments against this build:
Many Retribution paladins will chose to go down the Protection tree in lieu of the choices beyond Divine Strength in Holy. Precision, which increases hit chance by 3%, requires 5 points in either Improved Devotion Aura or Redoubt. While the 3% hit increase is highly useful, I believe the cost is better offset with gear where possible. Throw five points into Improved Blessing of Might, and you have the classic 5/8/48 build (http://www.wowhead.com/?talent=sxZxhZEf0t0cuiIot).
A popular option for Retribution paladins is continuing down the Protection tree to Blessing of Kings and for some, continuing to Guardian's Favor and Improved Righteous Fury for the wipe save and tankin ability, respectively.
COMBAT:
PVP and raiding as a Retribution paladin are, as with most classes, slightly different.
In starting PVP, you want to have an Attack Power of 1300, a 23% Crit Rating, and a 79 Hit Rating. The latter gives you the 5% PVP cap to not miss with special attacks. This is much easier if you specc'd for precision. If, like me, you did not, then you can compensate with gear - mostly gems and the PVP armor rewards.
Edit: I have since moved to a more classic build (http://www.wowhead.com/?talent=sxZxhZgfcth0uiIot). It is still a mix for world PVP/PVE.
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PROTECTION
The Protection paladin talent build (http://www.wowhead.com/?talent=sZVMtIg0zMgqtV0x0h) maximizes stamina and armor, as would be expected for a tank. Thirteen points into Retribution give the Protection paladin Deflection (http://www.wowhead.com/?spell=20064) for an increased parry, Benediction (http://www.wowhead.com/?spell=20105) to offset the mana-starvation that happens when he outgears the mobs, and Pursuit of Justice (http://www.wowhead.com/?spell=44414) mostly for the mobility.