Helm of Blazing Glory drops from Baleroc, and it is certainly the best-itemized tank helm this tier for death knights, with parry and mastery, our two primary secondary tanking stats. You'll want to get the tier four-piece bonus, of course, but if you can get the other four pieces, you may strongly want to consider taking this helm over the tier helm.
Elementium Deathplate Faceguard is our tier 12 helm and requires a token off of Ragnaros. Unfortunately, the expertise on this piece makes it a lot less desirable than it might otherwise be, and you probably won't take this over the Helm of Blazing Glory unless you need it to keep your four-piece tier bonus (or said other helm refuses to drop).
Stoneheart Necklace is your VP option this tier, and with parry and mastery, it's very well itemized. It's probably a good bet to pick it up.
Firebound Gorget is the zone drop option from Firelands. There's some debate over whether it's better than the VP necklace. While it does have a lot more mastery (thanks in part to the fact that it doesn't waste itemization on strength), it also has expertise, which is as usual a lot less useful for death knights and often a deal breaker.
Elementium Deathplate Shoulderguards are your tier 12 shoulders. While they do have the dreaded hit rating (again, not incredibly useful for a death knight tank), you will probably want these if only so you make the four-piece bonus, especially if you're using Helm of Blazing Glory. On the plus side, they do have the most mastery of any option this tier. You can get these via a token off of Staghelm.
Spaulders of Recurring Flame drop from Alysrazor and balance dodge and parry rating relatively well. Still, you are probably going to need the tier shoulders for the bonus.
While Pauldrons of Roaring Flame do have both dodge and mastery, the itemization balances more toward dodge than mastery, making them not as awesome as they could be. Still, if you get these off Ragnaros before your tier token drops, they're a decent stopgap.
The Elementium Deathplate Chestguard, which can be purchased with VP, has a nice little balance of dodge and parry. You'll want to get it, if only for the tier bonus.
The Carapace of Imbibed Flame off of Beth'tilac is arguably better itemized than the tier chest, since it has mastery and some dodge rating, but you need that tier bonus, so you'll probably want to pass on this one.
Durable Flamewrath Greatcloak can be purchased at friendly reputation with the Avengers of Hyjal, the Firelands raid reputation. While it does have yucky hit rating, it's all the only cloak you can pull out of a raid this tier. Buy it and use it ASAP.
Bracers of Regal Force are your VP option, with lots of dodge rating and a bit of parry rating. At only 1,250 VP, they're a bargain, especially since they're BOE, which means you can have one of your alts buy them for you.
Bracers of the Fiery Path drop off of Majordomo Staghelm. While mastery and parry is a juicy combination, these bracers waste a lot of itemization budget on strength. Therefore, even with all that delicious mastery, Bracers of Regal Force will probably edge them out on pure mitigation.
Gigantiform Bracers are the VP DPS bracers, but hit rating and mastery rating are both technically tank stats as well. Still, hit rating isn't great for a tank DK, so pass on these for tanking and spend your VP on other options.
Elementium Deathplate Handguards have mastery and dodge in copious amounts and only cost 1,650 VP. Even if they weren't a tier set piece, they'd be a no-brainer. Pick these up.
Fireskin Gauntlets, off Lord Rhyolith, have mastery, but they also have hit rating, which almost immediately makes them less desirable. Stick with tier.
If you're still saving up for tier, you may be able to grab a set of Flickering Handguards from Baleroc in the meantime. They come in various flavors, with some combination of dodge, mastery, and parry rating. Still, you will be replacing them with tier gear eventually, if only for the set bonuses.
Girdle of the Indomitable Flame can be purchased once you are honored with the Avengers of Hyjal. It's another piece with a nice balance of dodge and parry, and it's certainly worth taking, since everyone needs a little avoidance.
Uncrushable Belt of Fury drops from Shannox, but alas, it wastes a good portion of its itemization on expertise. Therefore, despite its rather large bit of mastery, the reputation belt above will still edge in out in most cases.
Elementium Deathplate Legguards are your VP-purchased tier option, and with copious amounts of both mastery and parry rating, they are also very well-itemized. Buy them for the stats; keep them for the set bonus.
Lavaworm Legplates drop off of Alysrazor, but with way too much hit rating, they just aren't even close to worth it compared to tier leggings even without taking set bonuses into account.
Legplates of Frenzied Devotion drop off Shannox and have dodge and parry rating. They're not horrible, but again, you want your set bonuses and the tier legs are very well-itemized.
Mirrored Boots are created with one of the blacksmithing patterns that drops in Firelands. With parry and mastery rating, they are just about perfect for a death knight tank, and you'll definitely want to get a set made.
Cracked Obsidian Stompers drop from Lord Rhyolith. They have a nice huge chunk of dodge rating, but the expertise on them definitely makes them inferior to the Mirrored Boots.
Adamantine Signet of the Avengers can be purchased at exalted with the Avengers of Hyjal. It does have hit rating, but it has a gem slot that can help make up for that.
Deflecting Brimstone Band is your VP option. With dodge and mastery rating, it's pretty solidly itemized and definitely worth picking up.
Theck's Emberseal is a raid drop option, but considering both your other options have better stats and are easy to get, you're better off selling this drop for gold and grabbing the other two.
Stay of Execution can be purchased at revered with Avengers of Hyjal. The chunk of dodge is definitely nice and worth it. What you will want to watch out for, though, is proper use of the on-use ability. Essentially, you'll want to save it for a big incoming spike of damage on a boss. Once the spike is over, you will take more damage, but the basic idea is that your healers should be able to heal through a little easier than if you'd take all the damage during the damage spike phase.
Spidersilk Spindle drops from Beth'tilac, as the name suggests. Not only does it have that nice, precious mastery, but it offers a quick damage shield when your health drops low.
Scales of Life is a Firelands zone drop, and there is some debate about how good it is. The proc is surprisingly compatible with death knight tanking. You can grab the healing charges from overhealing with Death Strike, and when you use it, the healing does get benefits from such abilities as Vampiric Blood. Unfortunately, since it has stamina, there's some argument that it isn't as good as the other two trinket options. Generally, I'd say you're best off using this one if you can't get the hang of use Stay of Execution's ability well, or if you prefer to have a nice little extra self-heal waiting in the wings.
Deathclutch Figurine remains your only tanking relic option. Luckily, it's relatively decent and doesn't cost that much VP.
Sulfuras, The Extinguished Hand may be your best bet for a tanking weapon. It has a good chunk of mastery, some gem slots, and higher DPS than any other two-handed melee weapon in game at the moment. You will have to down Ragnaros to get it, however, so it may take a while to grab.
Skullstealer Greataxe is another decent tank weapon. It also has mastery, and the haste isn't a completely worthless stat for tanks either, though certainly less valuable than others. It drops off Shannox, so you have a decent chance of grabbing it early.
Zoid's Firelit Greatsword is another option here, but it doesn't really have any stats that specifically scream tank. You can grab it if you just need the extra threat of a new weapon, but the other two weapons will edge it out for tanking purposes.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.