Neckpieces are tricky things, fortunately there are a lot to choose from. It's all up to taste. I'm skipping the Agility blues here like Bone Chain Necklace from the Black Stalker in Heroic Underbog. The +Hit is nice, and so is the Attack Power, but to be honest -- Agility does little for you. The awesome part is, there are lots of upgrades in Karazhan. Although your ultimate goal should be the Mithril Chain of Heroism from the Chess event.
Guardian's Pendant of Triumph - For Those Who Like to Fight
Yes, another PvP item. Sorry, but the sad fact is that great Retribution gear comes from PvP. I highly recommend this one because it's purchasable with Honor and doesn't require any Personal Ratings, so it's essentially a freebie. The yellow socket can be filled with pure crit. You can also ignore the socket bonus if you don't have a helm with a Meta gem and put +Strength instead. Because this is a Guardian, or Season 4, epic, do not hesitate to place an epic gem in the socket. This item will serve you well for a while.
Choker of Repentance - For Those Who Like to Shop
This is the only amulet in the game that combines both Strength and Spell Damage. Clearly built for Retadins, it's a decent item that you can buy if you have the money and the good fortune to find it at the Auction House. It should be relatively cheap, too, because very few classes want it. Best for Alliance Retadins, who don't have the juicy Seal of the Martyr yet and still rely on Seal of Command for raid DPS.
Haramad's Bargain - For Those Who Do the Daily Grind
Requires Exalted status with the Consortium. It has Strength (which is the only reason it makes this list). Don't grind for this item, as there are better out there, but if you're already Exalted or near it, this little bauble wouldn't hurt. But it honestly isn't much better than Soldier's Dog Tags from the Blood Furnace or even the crit-happy but Strength-less Adamantine Chain of the Unbroken from the Slave Pens.
Shattered Sun Pendant of Might - For Those Who Do the Daily Grind
I know. It's another one of those Agility items. But 64 Attack Power is nothing to sneeze at, and the proc is pretty decent, particularly if you're Aldor. Besides, everyone and his uncle is Exalted with the Shattered Sun Offensive nowadays, anyway, since those guys are so easy to please.
Alright, unlike the numerous choices you have with amulets, there are just a few key items for your back. And again, for some reason, there are a ton of Agility cloaks out there. Even the so-called Blood Knight War Cloak is an Agility item, which makes me roll my eyes. Agility is cool and all, but what you really want is Strength and crit.
Capacitus' Cloak of Calibration - For Those Who Like Instance Gratification
I know it's blue. But look at it! Strength, Stamina, and um, yeah, Agility, too. It's the baby version of the Razor-Scale Battlecloak from Morogrim Tidewalker. Thankfully, you don't need to go into Serpentshrine Cavern for this one, as it's easily farmed in Normal or Heroic Mechanar. With 5/5 Divine Strength, this is about as good as the Blood Knight War Cloak, which doesn't scale with Strength. So save those Badges.
Cloak of Darkness - For Those Who Feel Crafty
Leatherworkers Exalted with the Violet Eye can craft this excellent cloak for you. The blue socket can be socketed with a Sovereign gem (Strength and Stamina) or ignored for pure Strength. As an added bonus, this is one of the best cloaks with which to leave the graphic on. It's black and gold and badass.
Dory's Embrace - For Those With Badge Bravado
Did I say save those Badges of Justice? Yes I did. Because you'll need 60 of them to get this beauty. Sure, it's got Resilience, but it has decent crit, Attack Power, and the rare Armor Penetration. Because the main source of Retadin damage (pre-Wrath, anyway) is our white damage which is mitigated by Armor, the 112 Armor Penetration is pretty darn good.
Unlike other items that fill this slot for other classes, Paladins are gimped because Librams have exactly 0 stats. They have nice gimmicky effects, but otherwise, these are all arbitrary and swappable since they're all conditional depending on the ability you use. This is also one slot where PvP-bought items will do exactly jack for you since all they confer is Resilience.
Libram of Righteous Power - For Those Who Quest
Obtained in the last quest from a quest chain in Shadowmoon Valley, this can be picked up while leveling. It's not bad, and has been buffed significantly from its laughable original form.
Libram of Avengement - For Those Who Feel Heroic
The best libram for Blood Elf Paladins -- even for endgame raiding -- this drops off The Maker in Heroic Blood Furnace. It's almost like a constant 2.39% boost to your crit if you're on the ball with your Judgements.
Libram of Divine Judgement - For Those With Badge Bravado
Alliance Paladins have got the edge here because this libram only works with Seal of Command. Available for 20 Badges of Justice from G'eras in Shattrath.
Hooray. You can pick two from the list below. Fortunately, there are just a lot of rings out there to choose from. These are just some of my favorites, and because I'm a real sucker for Strength.
Nexus-Prince's Ring of Balance - For Those Who Feel Heroic
Despite the name, it doesn't drop off the Nexus-Prince in Mana-Tombs but his dog Yor, a boss that can be summoned by players on the Mark of the Nexus-King quest line. He also drops Shaffar's Band of Brutality, which has +Hit, crit, and equivalent Attack Power (without Divine Strength).
A'dal's Command - For Those Who Do The Daily Grind
This ring is nicely coupled with the Nexus-Prince's Ring of Balance, and obtained at Exalted status with the Sha'tar.
Of course, it has exactly the same +Strength as the Acrobat's Mark of the Sha'tar, which is a reward from a quest chain in Shadowmoon Valley. So you can pick that up as an easier alternative.
Eye of the Stalker - For Those Who Feel Heroic
This doesn't have Strength but pure Attack Power equivalent to 30 Strength. This drops off the Black Stalker in Heroic Underbog. For fun, you can match this with the identical Ring of Ghoulish Delight from the Horseman during Hallow's End.
Heavy Felsteel Ring - For Those Who Feel Crafty
Jewelcrafters can craft this item relatively cheaply. It grants 25 Strength, which is a considerable amount for a ring and is better than some of the aforementioned epics.
Band of Celerity - For Those Who Like Instance Gratification
Haste on a ring! Anything that improves Haste is pretty good, since it directly increases our white damage DPS. Drops off the first boss in Normal Magister's Terrace.
Reaver's Ring - For Those Who Feel Heroic
This moderately good ring with Strength and crit can be looted from the chest in Heroic Hellfire Ramparts, after defeating Nazan. You can also consider visiting Swamplord Muse'lek in Heroic Underbog for the Weathered Band of the Swamplord, which has less Strength but has Intellect.
Ring of Reciprocity - For Those Who Like to Shop
Doom Lord Kazzak drops this BoE ring which you can chance upon at the Auction House, provided your server bothers to kill the loud-mouthed demon these days. Even though it doesn't have raw Strength, it has +hit, crit, and pretty high Attack Power.
Angelista's Revenge - For Those With Badge Bravado
Yes, it's another one of those annoying Agility items but it's also one of the few Armor Penetration rings in the game. And we like Armor Penetration, yes, we do. [EDIT: various commenters] Just to be clear, though, Paladins get a high coefficient from Agility (as much as Shamans), and I've been remiss in knocking it as a stat. It still falls behind Strength in item valuation, but not to be scoffed at, as I've wrongly made it appear.
Guardian's Band of Triumph - For Those Who Like to Fight
Unfortunately, this requires a 1650 Personal Rating, so it's not so easy to get. You can settle for last season's Vindicator's Band of Triumph, which has less stats but doesn't require any Arena participation. I mention these rings because they have the delectable Armor Penetration, despite their shortage of Strength.
Ah, finally. Trinkets. Here's where we can have a little fun, even though our primary goal is increasing your Retadin DPS. Unlike other slots, trinkets don't necessarily have raw stats but often have on-use effects or interesting procs. There are just a few we can choose from that really contribute to Retribution's performance, but it's a fun slot to fill regardless.
Darkmoon Card: Crusade - For Those Who Like to Shop
While not strictly a shopping item, since it's obtained through a hand-in quest during the Darkmoon Faire, the cards for the Blessings Deck can be bought at the Auction House. This is one of my personal favorites, and doesn't require grinding instances or anything. The great thing about this card is that it procs off both melee attacks and spells which, voila, Retadins both use during combat. It's fairly easy to keep full stacks of both buffs during an encounter, increasing your DPS as the fight drags on. Did I mention this is one of my favorites? Yes, I love this trinket.
Bloodlust Brooch - For Those With Badge Bravado
Another one of my favorite items, this item has awesome raw Attack Power but what makes it shine is its Use, which should be triggered as often as possible and in conjunction with Avenging Wrath. Use both of them together and watch your DPS spike big through the roof. I drink Haste Potion during these times for more face-smashing goodness. You can also opt to get the Empty Mug of the Direbrew when Brewfest rolls around, which is identical, to save you Badges.
Abacus of Violent Odds - For Those Who Feel Heroic
This is a great trinket that's gimped only because it shares the same cooldown as the Bloodlust Brooch. But, it stacks with Haste Potion and you can keep the pain train going by popping this right after the cooldown effected by activating Bloodlust Brooch.
Shard of Contempt - For Those Who Feel Heroic
One of the new cool trinkets from Heroic Magister's Terrace, this drop from Priestess Delrissa has a pretty cool proc, which can be your cue for Bloodlust Brooch or the Abacus. On the other hand, there's minimal impact to be felt from the Expertise, although it does help somewhat.
Figurine - Khorium Boar - For Those Who Feel Crafty
If you're a Jewelcrafter anyway, you can look at the Khorium Boar, which confers a high Attack Power. It's not very useful... having a pig pop out every 5 minutes is good for some giggles but not really eye-popping DPS. Still, it's an option. 84 Attack Power isn't bad at all.
[EDIT: Madgoat] Hourglass of the Unraveller - For Those Who Like Instance Gratification
How could I forget?!? One of the best trinkets pre-Karazhan drops of Aeonus in the Black Morass. This has a relatively low proc rate of 10% off your own crits, but when it procs, it boosts your DPS significantly, especially coupled with Avenging Wrath.
[EDIT: Madgoat] Assassin's Alchemist Stone OR Alchemist Stone - For Those Who Feel Crafty
These bind-on-pickup items exclusive to Alchemists are a boon for potion-chugging Retribution Paladins who will run out of mana on even medium-length fights. Whether you want to go for a significant jump in Attack Power or spread out your stats a little bit is up to you.
There are several other options that you can pursue for the trinket slots, but the ones outlined above are best for pure DPS. I didn't list down the Battlemaster trinkets such as the Battlemaster's Cruelty and Battlemaster's Determination, even though they contribute to overall DPS with Attack Power and crit because the Use is pretty boring. You will almost never use it in a party or raid situation -- even less than a pig. At least the pig chews on your opponents. There's also the Skyguard Silver Cross from Exalted with the Skyguard, but the bonus aside from Attack Power isn't particularly useful in dungeons.
That's it. You've filled out your equipment slots. Now go enchant all you gear and make your way to Karazhan. What's that? You don't know what enchants to put on all your gear? Fear not, I'll be back with another installment of The Light and How to Swing It just to talk about all the stat boosts you can get from permanent enchantments and consumables. I did say I like to drink lots of Haste Potions, right? Well, start hoarding. See you next week.