The August Celestials
At honored, you'll be able to buy cloaks from the August Celestials for 1250 JP each. Ribcracker's Cloak has both haste and hit rating, making it an excellent choice for both varieties of DPS death knight. Cloak of the Silent Mountain offers parry and expertise rating for a tank. Reforge the expertise into mastery, and you'll have a pretty solid tanking cloak. Also available at honored, for 2200 JP, are Leggings of Ponderous Advance. This one will probably need some reforging, depending on your spec, but will serve you well as DPS until you get a better heroic dungeon drop.
At revered, you can buy bracers for 1250 VP. DPS get the Braided Black and White Bracer. Convert critical strike or expertise to haste as needed, and you're good to go with these. Tanks get the Battle Shadow Bracers. You can convert the hit to mastery for a solid piece of tank gear.
You can also buy gloves for 1750 JP. Streetfighter's Iron Knuckles are a solid choice for DPS, though frost will want to reforge the critical strike rating. Gloves of the Overwhelming Swarm, which have parry and mastery, are about the best itemization a death knight tank could hope for.
You can also buy boots for 1750 JP. Tankiss Warstompers offer critical strike and expertise for the DPS death knight, and thus are probably due some reforging. Tanks can buy Yu'lon Guardian Boots and reforge some of that dodge to mastery as needed.
At honored, 1250 JP will get you Serrated Forearm Guards, which, with expertise and mastery, could technically pass for both DPS and tanks, with the expertise reforged to parry or haste as appropriate for the spec. You can also get amulets for 1250 JP each. Triumphant Conqueror's Chain is the DPS option, while Gorget of Usurped Kings is the tank option. Both will likely need reforging to be optimal for death knights.
Also worth noting at honored the Mogu Rune of Paralysis. This trinket is arguably relatively inferior because of an on-use that is more novelty than utility, but the mastery is decent for both tanks and frost DPS. If you need a quick ilvl boost and you're already honored, you can pick this up easily if nothing else.
At revered, you can buy chest armor for 2250 JP. Dawnblade's Chestguard is a solid DPS option that will let you get to your hit and expertise caps that much easier. Cuirass of the Twin Monoliths is your tanking option, and while not well itemized for death knight tanks can be fixed up with a bit of reforging of dodge or expertise to mastery as needed.
Revered also brings rings at 1250 VP each. Ring of the Golden Stair is the DPS option, while Alani's Inflexible Ring is the tank option. Again, neither is optimally itemized, but can be fixed with some clever reforging.
Finally, shoulders can be purchased at revered for 1750 VP. Stonetoe Spaulders are the DPS option, while Shoulders of Autumnlight are the tank option. Both will need some reforging.
One other thing to watch out for on the Golden Lotus is the quests. A quest honored gives you a cloak reward. At revered, a quest gets you a chest piece, and at exalted, you'll be able to get an epic necklace. So keep up the grind and you will be rewarded.
At honored with the Klaxxi, you'll get the chance to purchase the Chestplate of the Stone Lion for 2200 JP. Again, this should work well for both tanks and DPS. You can reforge the hit to parry if you're a tank, or reforge either hit or mastery to haste for DPS, depending on your stat needs. If you're a blacksmith, honored with the Klaxxi will let you purchase some nice weapon and armor patterns as well.
At revered, you'll be able to purchase amulets for 1250 VP. Bloodseeker's Solitaire, with haste and mastery, is an amazing DPS neck for frost DPS, while unholy will probably want to reforge the mastery. Paragon's Pale Pendant is the tank option. Reforge the hit to mastery, and you'll be good to go.
Also at revered are legs for 2200 VP. Kovok's Riven Legguards are the tank option (though badly itemized), and Legguards of the Unscathed are your much better itemized DPS option.
Finally, The Klaxxi let you purchase belts for 1750 VP. Klaxxi Lash of the Rescinder, with critical strike and mastery, is slightly less than well itemized for DPS, but can be salvaged if you reforge the right stat to haste. Klaxxi Lash of the Consumer can be improved for tank death knights by reforging the hit to mastery.
Exalted with the Klaxxi also brings some good opportunities. You can buy the Amber Espada of Klaxxi'vess, or the Amber Flammard of Klaxxi'vess. At item level 463, you'll still find better in raids, but if you're having bad drop luck in heroic dungeons, these weapons are just what the doctor ordered.
At honored with the Shado-Pan, you'll be able to pick up Wall Breaker Gauntlets for 1750 JP. With haste and expertise, they're very well itemized for DPS death knights. You'll also be able to pick up a ring for 1250 JP. Signet of the Slumbering Emperor is well itemized for unholy DPS, though frost death knights will want to reforge the critical strike rating. Thunderstone Ring is the tank option. Reforge the hit to mastery, and you're golden.
At revered, you can pick up a helmet for 2250 VP. Yi's Least Favorite Helmet features dodge and mastery for the tank death knight. You will probably want to reforge the dodge to parry. Voice Amplifying Greathelm is the DPS option. Critical strike and expertise aren't really optimal for either DPS spec here, so you'll want to do some reforging of critical strike to haste.
For 1250 VP, you can pick up a cloak. Yi's Cloak of Courage is the tank option, and with parry and mastery, is about as good as you can get. Cloak of the Dark Disciple is the DPS option, but with critical strike and mastery, isn't very well itemized for either DPS spec.
Finally, for 1750 VP, you can grab a trinket. With a ton of strength and haste on use, Iron Belly Wok is actually pretty good for DPS. Lao-Chin's Liquid Courage is similarly awesome, with stamina and mastery on use.
Who do I grind first?
Since essentially all factions offer decent options, it's difficult to say which faction want to focus on first. The Klaxxi's exalted weapons are a nice insurance option if you have crummy heroic drop luck, so my first instinct is to focus on them, but a lot of what you'll grind probably depends on what heroic dungeon drops you get and what slots you still need to grab. Mostly, keep running scenarios and dungeons for gear, JP, and VP, stay light on your feet, and be ready to switch focus as your gearing needs require.
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.