I have tried to come up with a list of the best pre-raid DK tank gear, the base of it was stolen from World of Warcraft - English (NA) Forums -> DK Tank Gear Guide: Uncritable before Naxx and a lot of credit is due to Ragnarök for compiling the initial list. However that list doesn't appear to be being updated, so I think it is worth doing the same thing again here.

Of course the most important thing to worry about is getting Defense Capped, so any gear that works to that end will trump anything that does not.

All of the items listed have been listed in the order of a rating system I devised based upon the relative value of each of the relavent stats from Rawr TankDK. All sockets have been filled based on socket color NOT necessarily the best gem that could be used (best available is to hard to quantify as it is deriviative of all of your other gear). The final note is that if you are not Def capped the rest doesn't matter so an item that rates lower may still be 'better' for you if you are not at the Def cap.

Relative stat values given by rawr (threat generation value has been ignored):
Stamina - 76.73
Strength - 5.2
Agility - 37.23
Resiliance - 25.39
Dodge - 30.23
Parry - 20.79
Armor - 14.04
Defense - 26.91*

Notes:
*Defense was not given by Rawr and is instead calculated by the formula Def=[(Parry value*.399)+(Dodge*.319)]*1.5. Which is the best mathimatical value I was able to find for Def relative to how it effects other stats.

Expertiese should have some defensive value in that it helps reduce parry jibbing, but I couldn't find a reliable number. However whatever number it does have I expect to be relatively low.

Besides allowing a determination of best in slot item comparison, the rating number can also be used to determine the most adventagious item in any slot to go after. By creating a rating for your current gear (just multiply the items value by the relative value of that stat given above), and then subtracting that number from the rating value in this list you can see the upgrade value for each of the items. Divide that by the amount of gold/rep/runs/ect it takes to get the upgrade and you will know which to go after first.

Head
Enchant: [Arcanum of the Stalwart Protector] Requires Argent Crusade - Revered
[Tempered Titansteel Helm] - Blacksmithing - Rating 41,609
[Ground Tremor Helm] - From Moorabi ( Gundrak) - Rating 35,142
[Arcane-Shielded Helm] - From Grand Master (H Nexus) - Rating 36,761
[Armored Titanium Goggles] - Requires Engineering - Rating 36,508
[The Crusader's Resolution] - Quest reward from The Crusaders' Pinnacle - Quest - World of Warcraft - Rating 31,439
[Tempered Saronite Helm] - From Blacksmithing - Rating 26,660


Neck
[Titanium Earthguard Chain] - JC - Rating 13,180
[Chained Military Gorget] - 25 Badges - Rating 7,823
[Shadowseeker's Pendant] - H OK (Jedoga Shadowseeker) - Rating 6,805
[Pendant of the Nathrezim] - H CoS (Dark Runed Chest) - Rating 6,452

Shoulders
Enchant: [Greater Inscription of the Pinnacle] Requires The Sons of Hodir - Exalted
[Wapach's Spaulders of Solidarity] - BoE From a number of instances trash - Rating 33,130
[Iron Dwarf Smith Pauldrons] - From General Bjarngrim (H HoL) - Rating 31,592
[Pauldrons of the Colossus] - From Drakkari Colossus (H Gundrak) - Rating 31,507
[Crusader's Square Pauldrons] - BoE from The Culling of Stratholme - Rating 30,187
[Tempered Saronite Shoulders] - Blacksmithing - Rating 28,018
[Pauldrons of Reconnaissance] - From HoS (No Mob listed on WoWHead) - Rating 27,713

Back
Enchant: [Formula: Enchant Cloak - Titanweave]
[Durable Nerubhide Cape] - LW BoE - Rating 9,555
[Cloak of the Enemy] - H Nexus (Commander Kolurg and Commander Stoutbeard) - Rating 8,391
[Cloak of Peaceful Resolutions] - Wyrmrest Accord - Honored - Rating 8,195

Chest
Enchant: Enchant Chest - Greater Defense - Spell - World of Warcraft
[Heroes' Scourgeborne Chestguard] - Normal VoA - Rating 46,299
[Sun-Emblazoned Chestplate] - H HoS (Sjonnir The Ironshaper) - Rating 43,120
[Ziggurat Imprinted Chestguard] - H Drak (The Prophet Tharon'ja) - Rating 42,266
[Breastplate of the Solemn Council] - Wyrmrest Accord - Revered - Rating 41,688
[Ivory-Reinforced Chestguard] - Requires The Kalu'ak - Honored - Rating 34,655

Wrist
Enchant: [Formula: Enchant Bracer - Fortitude]
[Bracers of Dalaran's Parapets] - 60 Badges - Rating 22,565
[Bracers of the Herald] - Herald Volazj (H Old Kingdom) - Rating 21,571
[Hateful Gladiator's Bracers of Triumph] - 31,000 Honor - Rating 20,458
[Bindings of Dark Will] - Salramm the Fleshcrafter (H Strath) - Rating 19,943
[Tempered Saronite Bracers] - Blacksmithing - Rating 15,991

Hands
Enchant: [Formula: Enchant Gloves - Armsman]
[Heroes' Scourgeborne Handguards] - Normal VoA - Rating 30,841
[Fireproven Gauntlets] - Kirin Tor - Exalted - Rating 30,055
[Horn-Tipped Gauntlets] - H Gundrak (Gal'darah) - Rating 28,602
[Gauntlets of Vigilance] - Quest reward The Reckoning - Quest - World of Warcraft - Rating 26,642
[Daunting Handguards] - Blacksmithing - Rating 25,035
[Tempered Saronite Gauntlets] - Blacksmithing - Rating 24,071

Waist
[Ancient Aligned Girdle] -Anub'arak (H Azjol-Nerub) - Rating 28,785
[Hateful Gladiator's Girdle of Triumph] - 49,600 Honor - Rating 28,582
[Waistguard of Living Iron] - 40 Badges - Rating 28,249
[Waistguard of the Risen Knight] - BoE from Drak - Rating 26,206
[Tempered Saronite Belt] - Blacksmithing - Rating 20,020

Legs
Enchant: [Frosthide Leg Armor]
[Bolstered Legplates] - Cyanigosa (H VH) - Rating 40,094
[Special Issue Legplates] - Requires Argent Crusade - Honored - Rating 36,051
[Daunting Legplates] - Blacksmithing - Rating 35,492

Feet
Enchant: Enchant Boots - Greater Fortitude - Spell - World of Warcraft
[Tempered Titansteel Treads] - Blacksmithing - Rating 32,019
[Greaves of Ancient Evil] - H OK (Herald Volazj) - Rating 30,005
[Sabatons of Draconic Vigor] - Wyrmrest Accord - Revered - Rating 29,217

Finger
Enchant: Enchant Ring - Stamina - Spell - World of Warcraft - Only for enchanters of course
[Titanium Earthguard Ring] - JC - Rating 8,744
[Signet of the Accord] - BoE (From OS) - Rating 7,350
[Woeful Band] - Maiden (H HoS) - Rating 6,380
[Dragonflight Great-Ring] - Eregos (Normal Occulus) - Rating 5,608
[Gal'darah's Signet] - High Prophet of Akali (Normal Gundrak) - Rating 5,247

Trinket
[Seal of the Pantheon] - Loken (Normal HoL) - Rating 10,103
[Figurine - Monarch Crab] - Only if you are a JC - Rating 9,308
[Essence of Gossamer] - Hadronox (H Azjol-Nerub) - 8,517
[Valor Medal of the First War] - 40 Badges - Rating 4,227

Notes:
1)On use trinkets are assumed to be used as soon as their cool down is ready
2) Procs are not modled


Weapon
Enchant: Rune of the Stoneskin Gargoyle - Spell - World of Warcraft
[Saliva Corroded Pike] - Moragg (H VH) - Rating 10,806
[Whale-Stick Harpoon] - Requires The Kalu'ak - Revered - Rating 10,472
[Colossal Skull-Clad Cleaver] - Loken (H HoL) - Rating 9,691
[Sword of Justice] - H HoS Tribunal Chest - Rating 8,904
[Titansteel Destroyer] - BoE Blacksmithing - Rating 8,701
[Axe of Bloodstained Ice] - Quest reward - Rating 7,763

Horde - Cradle of the Frostbrood - Quest - World of Warcraft

Alliance - Sindragosa's Fall - Quest - World of Warcraft

Sigil
Sigil of the Unfaltering Knight - Thottbot: World of Warcraft - 15 Badges (Sorry I couldn't get a tooltip that worked)

Gems
[Thick Autumn's Glow] - Defense
[Solid Sky Sapphire] - Sta
[Perfect Subtle Bloodstone] - Dodge

Meta gem
Unless you are trying to eek out the last few Def point to get capped, [Austere Earthsiege Diamond] is probably the best bet. There is some debate on the issue, but this looks to be either the best or at least in the top 2 of Meta gems.

Updated.

I didn't include all of the Black smithing items since in some instances there were better items already on the list that were what I would consider 'easy to get' things. But thanks for the suggestions.

While potentially very expensive, DK's can buy [Wapach's Spaulders of Solidarity] from the AH.

Wrist: [Bracers of the Herald] (Heroic Ahn'kahet)
Trinket: [Valor Medal of the First War] (40 Emblems of Heroism)
Hands: [Heroes' Scourgeborne Handguards] (60 Emblems of Heroism)
Chest: [Heroes' Scourgeborne Chestguard] (80 Emblems of Heroism)
Feet: [Tempered Titansteel Treads] (BS Crafted) I don't think any tank would actually use these, but maybe useful if short wyrmrest rep?

Most of the starting tanking gear has more defense than the raid gear so using yellow gems for defense might be overkill. It might be better to put hit rating in those slots.

Note that [Bracers of Dalaran's Parapets] are BoE. While not for everyone, it's well possible to buy them on AH or donate them to an alt.

[Signet of the Accord] should pop up on the AH regularly too.

If you're low on Def there is [Axe of Bloodstained Ice] from a quest in icecrown (I think) as well. although your threat will suffer.

Until at least honored with Sons of Hodir, you go for the following shoulder enchant:

[Greater Inscription of the Gladiator] - for a mere price of 10,000 honor in Orgrimmar / Stormwind

The red gem should actually be either 8dodge/12stam or 8exp/12stam.
The yellow gem should be either 8hit/12stam or 8def/12stam.

I really don't think anyone should gem for avoidance but some think its OK and some think its a wasted socket.

It depends on your gear. DK tanks should shoot for defense cap, melee hit cap, and expertise soft cap. They can use gem slots to round out their gear and make sure they continue to satisfy that criteria as they replace individual pieces. After you have those concerns met you can debate if x amount of avoidance is better than y amount of health. For example, if you are over the hit cap or have extremely low health, you should swap out a +16 hit gem for one of the hybrid gems with stam or dodge depending upon which you find more valuable.

I think with that objective in mind, it only makes sense to list the red/blue/yellow gems people should shoot for, and if they find that they need to shift stats around at an even small level, they can go for the hybrid gems.

I'm guessing you mean something like this...

Red: 8exp/12stam - 8dodge/12stam - 16expertise - 16dodge
Yellow: 8hit/12stam - 8def/12stam - 16hit - 16defense
Blue: 24stamina - 8hit/12stam - 8exp/12stam - 8def/12stam - 8dodge/12stam
Prismatic: Any of the previously stated.

I suppose it does make more sense to just list the gems you would use as a DK tank instead of the best because there isn't a "best".

I would like to add the following to the list of items.
[Sword of Justice] Tribunal Chest in H HoS
[Cloak of the Enemy] Commander in H Nexus
[Pendant of the Nathrezim] Dark Runed Chest in H CoS
[Shadowseeker's Pendant] Jedoga Shadowseeker in H OK
[Ziggurat Imprinted Chestguard] The Prophet Tharon'ja in H DTK
[Sun-Emblazoned Chestplate] Sjonnir The Ironshaper in H HoL
[Greaves of Ancient Evil] Herald Volazj in H OK
[Gauntlets of the Water Revenant] Ichoron in H VH

You may want to include:
Weapon: Argent Skeleton Crusher - Argent Dawn - Revered

Neck: Betrayer's Choker - Betrayal quest - Zul'Drak