So this is my attempt at a "guide", which I wrote a while ago but didn't post as there was already a "list". It includes the type of recommendations that others have asked for. Of course, at this point the comments are just my own, but I could improve them with feedback and consensus.
General Theory
In Burning Crusade, uncrittable was easy, almost automatic, before stepping foot in the first challenging instance. It was uncrushable that became the focus of gear guides and upgrade strategy pre-Kara. That's all changed in WotLK. The new defense requirement - 540 total defense, 689 defense rating from gear - puts a heavy focus on achieving uncrittable before being put to the test.
Blizzard has thus changed the game for item enhancement. Rather than focusing solely on stamina for gems, the need to gem for both stamina and defense (plus some nice new socket bonuses) make a balanced approach viable. Likewise for enchants, defense may be the early favorite for many slots, with several other options open once 540 is achieved.
One thing that hasn't changed is the baseline stamina / defense ratio for gems. Basically, Blizzard values defense rating at 150% that of stamina when itemizing gem sockets. This can be seen when, for example, swapping a Solid Majestic Zircon for a Thick King's Amber costs 30 stamina for a gain of only 20 defense rating, or likewise swapping a Solid Majestic Zircon for an Enduring Eye of Zul costs 15 stamina for a gain of 10 defense. Of course socket bonuses should be considered when planning such a swap.
This ratio often doesn't apply to enchants. When the options for an item enchant skew one way or the other, it's generally best to pick the one favored by the imbalance. For example, the BC enchants for bracers offered either 12 stamina or 12 defense rating. This ratio clearly favors defense rating, as it's relatively "cheaper" (in terms of stamina lost) to put defense rating here than it is to swap out a gem. This is also true with the BC-era 15 defense enchant to chest, which outweighs the new 18 stamina armor kit (and of course the WotLK defense enchant trumps both).
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Gemming
Gems are available for most any stat, but most paladins will favor defense and stamina as the primary options for yellow and blue, respectively. There may be more controversy for red slots, with strength, dodge rating, and parry rating available, but the synergy of threat and mitigation offered by strength makes it an initial favorite. It's also unaffected by the diminishing returns added to dodge and parry rating, which will punish those who chose those gems when combined with the high stat values surely to appear on later WotLK gear.
Red Gem Slot
Bold Cardinal Ruby, +20 Strength, Crafted (Jewelcrafting)
Bold Scarlet Ruby, +16 Strength, Crafted (Jewelcrafting 390)
Sovereign Dreadstone, +10 Strength and +15 Stamina, Crafted (Jewelcrafting)
Sovereign Twilight Opal, +8 Strength and +12 Stamina, Crafted (Jewelcrafting)
Digren says, "Red offers gems for strength, dodge, and parry rating with equal units, which means they have very different benefits. Many tankadins will prefer strength for the combined threat and mitigation, and most of those will use a combo gem to push up stamina."
Blue Gem Slot
Solid Majestic Zircon, +30 Stamina, Crafted (Jewelcrafting)
Solid Sky Sapphire, +21 Stamina, Crafted (Jewelcrafting 390)
Enduring Forest Emerald, +8 Defense Rating and +12 Stamina, Crafted (Jewelcrafting)
Digren says, "Pay attention to the poor value of the Solid Sky Sapphire. With only +21 Stamina, it's under the 150% ratio defined for most gems. A piece with one red and one yellow gem slot, for example, would net only +21 stamina and +16 defense rating if pure blue and yellow gems were used in those slots. However, if two combo gems, the Enduring Forest Emerald, were socketed instead, the net is +24 stamina with the same defense rating."
Yellow Gem Slot
Think King's Amber, +20 Defense Rating, Crafted (Jewelcrafting)
Thick Autumn's Glow, +16 Defense Rating, Crafted (Jewelcrafting 390)
Enduring Eye of Zul, +10 Defense Rating, +15 Stamina, Crafted (Jewelcrafting)
Enduring Forest Emerald, +8 Defense Rating, +12 Stamina, Crafted (Jewelcrafting)
Digren says, "With the need to stack defense early in WotLK to be uncrittable, straight defense gems may be viable in yellow slots. Some may choose the combo stamina gems for more refined balance above 540 defense."
Any Slot
Bold Dragon's Eye, +27 Strength, Crafted (Jewelcrafting 375 Self Only
Thick Dragon's Eye, +27 Defense Rating, Crafted (Jewelcrafting 375 Self Only)
Solid Dragon's Eye, +41 Stamina, Crafted (Jewelcrafting 375 Self Only)
Digren says, "Jewelcrafter tanks have these great options to choose from. The need for early defense makes the Thick Dragon's Eye quite attractive, but the slightly-better-than-average ratio for the Solid Dragon's Eye tilts in its favor as well. Start with one or more defense rating gems, then migrate to stamina as your gear allows."
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Enchanting
Whether attained through enchanting, some other trade skill, or through purchased kits, the options for enchanting are much more varied than with gems. Unfortunately the strategy is less flexible, as the general rule is "if there's a WotLK enchant for defense rating, use it." Slots without a strong contender for best enchant have greater flexiblity, such as the continued option for threat enhancement in the hand slot, or the trade off for mobility on boots.
Head
Shoulders
Lesser Inscription of the Pinnacle, +15 Dodge Rating and +10 Defense Rating, The Sons of Hodir (Honored)
Greater Inscription of the Pinnacle, +20 Dodge Rating and +15 Defense Rating, The Sons of Hodir (Exalted)
Greater Inscription of Warding / of the Knight, +15 Dodge Rating and +10 Defense Rating, The Aldor / The Scryers (Exalted)
Heavy Borean Armor Kit, +18 Stamina, Crafted (Leatherworking 395)
Master's Inscription of the Pinnacle, +52 Dodge Rating and +15 Defense Rating, Crafted (Inscription 400 Self Only)
Digren says, "Inscribers, get your self-only armor buff here. The rest of us will keep using our BC inscriptions (as long as 8x Fel Armaments run less than 75g) until we've earned the incremental upgrade."
Back
Enchant Cloak - Mighty Armor, +225 Armor, Crafted (Enchanting 430)
Enchant Cloak - Titanweave, +16 Defense Rating, Crafted (Enchanting 435)
Enchant Cloak - Steelweave, +12 Defense Rating, Crafted (Enchanting 375)
Enchant Cloak - Dodge, +12 Dodge Rating, Crafted (Enchanting 300)
Lightweave Embroidery, Chance to cause 1000 to 1200 holy damage when you damage an enemy with a spell, Crafted (Tailoring 420 Self Only)
Swordguard Embroidery, Damage melee attacks sometimes increase your attack power by 300 for 15 sec, Crafted (Tailoring 420 Self Only)
Digren says, "The relatively new defense enchants take what used to be a weak enchant slot and make it quite good. There's little reason to take less than the best. Are there any tankadin tailors?"
Chest
Wrist
Enchant Bracers - Expertise, +15 Expertise Rating, Crafted (Enchanting 415)
Enchant Bracers - Greater Assault, +50 Attack Power, Crafted (Enchanting 430)
Enchant Bracers - Striking, +38 Attack Power, Crafted (Enchanting 360)
Enchant Bracer - Major Defense, +12 Defense Rating, Crafted (Enchanting 320)
Enchant Bracers - Greater Stats, +6 All Stats, Crafted (Enchanting 400)
Enchant Bracer - Fortitude, +12 Stamina, Crafted (Enchanting 350)
Enchant Bracer - Brawn, +12 Strength, Crafted (Enchanting 305)
Fur Lining - Attack Power, +114 Attack Power, Crafted (Leatherworking 400 Self Only)
Fur Lining - Stamina, +90 Stamina, Crafted (Leatherworking 400 Self Only)
Digren says, "Tankadin leatherworkers will go for their fur lining for a huge stamina gain. For the rest of us, the old BC defense rating enchant may be the best bet while gearing up, to be replaced with a threat enchant (probably greater assault) at the high end."
Waist
Digren says, "Poor tankadin engineers. They have to sacrifice the standard enchant, losing defense or stamina, to apply their profession to most slots, and their only unique slot has nothing of note for tanks."
Hands
Glove Reinforcements, +240 Armor, Crafted (Leatherworking 350)
Enchant Gloves - Expertise, +15 Expertise Rating, Crafted (Enchanting 405)
Enchant Gloves - Precision, +20 Hit Rating, Crafted (Enchanting 410)
Enchant Gloves - Crusher, +44 Attack Power, Crafted (Enchanting 425)
Enchant Gloves - Greater Assault, +35 Attack Power, Crafted (Enchanting 395)
Enchant Gloves - Armsman, +2% Threat and +10 Parry Rating, Crafted (Enchanting 435)
Enchant Gloves - Threat, +2% Threat, Crafted (Enchanting 300)
Heavy Borean Armor Kit, +18 Stamina, Crafted (Leatherworking 395)
Enchant Gloves - Major Strength, +15 Strength, Crafted (Enchanting 340)
Hand-Mounted Pyro Rocket, Allows you to deal 1035 to 1265 fire damage to an enemy at range, 1 minute cooldown, Crafted (Engineering 400 Only)
Digren says, "Two years ago, every paladin would have switched to engineering for a convenient pulling tool. Today, the young tankadins might start with the armor kit for a stamina boost, and switch to +threat as DPS players scale up their gear."
Legs
Frosthide Leg Armor, +22 Agility and +55 Stamina, Crafted (Leatherworking 425)
Jormungar Leg Armor, +15 Agility and +45 Stamina, Crafted (Leatherworking 405)
Nethercleft Leg Armor, +12 Agility and +40 Stamina, Crafted (Leatherworking 365)
Clefthide Leg Armor, +10 Agility and +30 Stamina
Jormungar Leg Reinforcements, +22 Agility and +55 Stamina, Crafted (Leatherworking 405 Self Only)
Digren says, "Leatherworkers get a leg up with their BoP pattern, but everyone eventually reaches Frosthide as the best, if expensive, leg enchant."
Feet
Enchant Boots - Greater Assault, +32 Attack Power, Crafted (Enchanting 440)
Enchant Boots - Tuskarr's Vitality, +15 Stamina and +8% Run Speed, Crafted (Enchanting 440)
Enchant Boots - Boar's Speed, +9 Stamina and +8% Run Speed, Crafted (Enchanting 360)
Enchant Boots - Greater Fortitude, +22 Stamina, Crafted (Enchanting 385)
Digren says, "As usual, controversy will erupt between those that choose Pursuit of Justice and the stamina enchant, and those that put the speed on their feet. Either are reasonable based on your choice of spec."
Shield
Finger
Enchant Ring - Assault, +32 Attack Power, Crafted (Enchanting 400 Self Only)
Enchant Ring - Stamina, +24 Stamina, Crafted (Enchanting 400 Self Only)
Digren says, "Enchanters get their self benefit here, with a much better stamina enchant to replace the now-defunct spell power options available in BC."
Melee Weapon
Enchant Weapon - Superior Potency, +65 Attack Power, Crafted (Enchanting 435)
Titanium Weapon Chain, 50% Disarm Duration Reduction and +28 Hit Rating, Crafted (Blacksmithing 420)
Enchant Weapon - Potency, +20 Strength, Crafted (Engineering 350)
Digren says, "Weapon slot has emerged as one of the weaker slots for WotLK enchants so far, with the BC-era Potency still seen as a viable option. Many may opt for the Titanium Weapon Chain. I expect testers to eventually determine how often and for how long a foe needs to disarm you to make it yield more threat than the raw attack power enchant."
