In the Borean Tundra, you'll find The Axe of Frozen Death. It's a very nice blue with the perfect stats for a Death Knight, and it's pretty straightforward to get: Just follow the basic recruitment quest for your side in either Valiance Keep or Warsong Hold. Eventually, you'll be sent out into the field to do a bunch of stuff, eventually ending in a group quest on either side that will get you the axe as one of your quest rewards. Alliance will get it from Last Rites, while the Horde will get it from Hellscream's Champion, a fedex type quest you'll get after finishing everything else Garrosh has for you to do.
If you'd like to stick to the Howling Fjord, you can pick up the Cragthumper, which is arguably a slight bit better than the axe for Death Knight tanking, since it has a good amount of stamina, as well strength to convert into parry rating. It's also much easier to get, requiring only a very basic starting quest on either side. Rescuing the Rescuers is the Alliance Quest, while Landing the Killing Blow is the Horde quest. If you're giving dual wielding a try here, you can pick up the Coldstone Cutlass from this quest instead, which should make a passable main hand weapon.
If you're looking for the best possible one-handed weapons, though, consider the Edge of the Tuskarr from Borean Tundra. This one has a slower speed, making it much better for dishing out the strikes and Blood Caked Blade procs. This you'll get from the Tuskarr themselves, namely the quest The Tides Turn. For a one-handed offhand, you want speed for triggering Killing Machine procs and the like. Luckily, you can also pick up a good off hand in Borean Tundra too, the Lobstrok Striker, which comes from rescuing tadpoles.
In the Borean Tundra, you'll be able to quest for the Mightstone Helm, which is a very nice Death Knight helm with plenty of our two main DPS stats, critical strike rating and strength. Alliance get it from The Hunt Is On, and Horde get it from the Trophies of Gammoth.
If you're in the Howling Fjord, you can grab the Runeplate Helm, but, as we said earlier, haste isn't our best stat by a long shot, and this helm has a good amount of it. Still, it'll do in a pinch, and is probably better than whatever you picked up in Outland. If nothing else, it does outdo the Mightstone Helm in pure strength. Alliance get it from Mission: Eternal Flame, while Horde get it from Adding Injury to Insult.
In the Borean Tundra, you have a few choices as far as shoulder armor goes. Chilled Pauldrons are completely devoid of Stamina, but do have a good amount of strength and critical strike rating. You can get them from Re-Cursive for the Alliance, or Neutralizing the Cauldrons for the Horde. Chilled Shoulderpads have a bit less strength, but a good chunk of stamina, which many levelers overlook to their own peril, and a bit more critical strike rating. They can be gained from Stop the Plague for the Horde, or There's Something Going On In Those Caves for the Alliance.
In Howling Fjord, Alliance will probably wanted to consider picking up the Feather-Lined shoulderpads, which offer as much strength as the Chilled Pauldrons and some hit rating, which many levelers also overlook. 5% hit or so while leveling works wonders on making sure your hits connect. The other Howling Fjord plate shoulder option is the Ramshorn-Inlaid Shoulders, but they suffer from the problem of haste rating. If you're Horde, you'll probably want to go to Borean Tundra for the best shoulders you can get.
In the meantime, I should also mention that tanks might want to do a little dungeon diving for some new shoulders some time in their early 70s. The quest Have They No Shame sends you into The Nexus, off Borean Tundra, to recover some lost research, with one of the rewards being Tundra Pauldrons. While said Pauldrons have slightly less defense rating than Cobalt Shoulders, and some shield block value, which is useless to us, they also have much more stamina and armor and a bit of dodge rating, which should make them a pretty clear tanking upgrade regardless.
In the Howling Fjord, you can pick up the Worgblood Berserker's Hauberk by assisting Ulfang via your faction's questgivers at the Steel Gate, which balances a good bit of strength with a good bit of stamina. Once again, though, your better options are going to be in the Borean Tundra.
The Battle Leader's Breastplate out of the Tundra is a DPSer's dream come true, with strength, agility, and critical strike rating in abundance. The Alliance gets it from Surrounded!, while the Horde gets it from What the Cold Wind Brings.... If you find yourself a bit low on stamina though, you might want to go after the Mightstone Breastplate, which has no agility, but almost as much strength and critical strike rating and a good bit of stamina. It's gained from Enemies of the Light for the Alliance and Bury Those Cockroaches! for the Horde.