If you've done a little bit of work on your Argent Crusade faction in Zul'drak and Icecrown, you've hopefully hit honored, meaning you can pick up a set of Special Issue Legplates. A very solid pair of defense legplates with over 100 stamina, these also have a chunk of hit rating and a red gem slot perfect for your favorite defense bearing gem.
If, for some reason, you aren't grinding Argent Crusade faction yet, or you're still in the "need every point of defense rating I can get" stage, you can pick up a pair of Daunting Legplates from a Blacksmith. They don't have quite as much stamina as the special issue, nor do they have hit rating or a gem slot, but they do have more defense rating and strength.
Here's one more reason to hit revered with the Wyrmrest Accord: Sabatons of Draconic Vigor blow away all comers for the title of awesome tank boots outside of a heroic or raid. I'm really suggesting that if you aren't revered with Wyrmrest Accord yet, you throw on a tabard and wheedle your way into a few level 80 dungeon runs. These boots and the above breastplate are more than worth it.
In a pinch, you can also unlock Dutchess Mynx in Icecrown and buy a pair of Toxin-Tempered Sabatons. But despite the fact that they're sold by our own faction, they have shield block on them, and thus aren't optimal for Death Knights.
One of your best options for a pre-heroic defense necklace is going to be from the Icecrown quest The Admiral Revealed. The Reinforced Titanium Neckguard has defense, dodge rating, and a red gem socket for your customizing pleasure.
Another solid option is the Amulet of Deflected Blows from Skadi the Ruthless in Utgarde Pinnacle. It has far more strength and stamina than the quest reward neck, and replaces the dodge with a good chunk of parry rating.
Oh, and if you remember Torta and Tooga from Tanaris, you might get a chuckle out of this: Apparently they've made their way to Northrend. Torta lost her choker though, since it drops off random level 78+ elites. If you're the one to recover it, it makes a decent option for a tanking neck. Just remember, come 3.0.8, the extra armor on it won't multiply with Frost Presence.
This is a place where choice is way too clear. Do the Wyrmrest Accord quests in Dragonblight and Borean Tundra, and you should easily have honored with the faction. Then, go buy the Cloak of Peaceful Resolutions.
Seriously, go do it. It's easy.
Most of your ring options are going to require some dungeon divings, but if manage to scrounge up a couple eternal earths, you can get a quick defense ring option from the a Jewelcrafter with the Stoneguard Band. The blue gem slot on the band would probably be a good place to stick an Enduring Dark Jade, as well. You can also find Tooga's Lost Toenail, a dropped bind on equip ring with some extra armor and defense.
If you can get some dungeon groups, you can grab a few other decent rings. The Dragonflight Great-Ring is about as good as it gets for pre-raiding tank rings, and can be grabbed from the last boss of the Oculus. As long as you're headed in there, pick up The Struggle Persists -- you'll need for the previously mentioned A Wing and A Prayer quest anyway. The Staunch Signet reward from that quest will make a great pair with this ring. If you can get a Gundrak group, the quest For Posterity will yield a Solid Platinum Band, which is nearly the twin of the Staunch Signet, but with parry rating instead of dodge rating.
If you want to get your defense by going the trinket route, you have one option before Naxxramas, which is the Seal of the Pantheon from Loken in the Halls of Lightning. Otherwise, Wrath-era tank trinkets are all parry rating and extra health and the like.
If you are looking for those last few points of defense rating in a trinket slot, though, you can always go back to Burning Crusade. As we mentioned last week, people are finding that they can solo themselves a Dabiri's Enigma or an Adamantine Figurine relatively easily at level 80.
Patch 3.0.8 and Tanking
Here's one more thing to keep in mind as you build your tanking gear set: relief for defense-starved Death Knights is coming. As you may recall our new Mike mentioning, Patch 3.0.8 will bring with it many tanking buffs, including the Rune of the Stoneskin Gargoyle, which provides 25 defense skill (That's skill, not rating) and 2% stamina on 2-handed weapons. If you don't mind giving up 4% parry, that's a nice little chunk of defense on your weapon that can give you the freedom to choose other stats for other slots.
Overall, as you can see, there's a lot of decent options that you can mix and match to hit that 540 defense plateau in Northrend, even without defense on your weapon. Good luck getting that tanking set together, and for my Unholy tank bretheren, may you never meet up with a group that tells you to "lol respec frost to tank, nub."