On Statistics and Gear choices
If you're having trouble figuring out how to figure upgrades, there's actually a very simple rule of thumb: Death Knight gear needs are very close to Warrior needs. DPS Warrior plate will do just fine for any Death Knight, so if you can remember nothing else, just remember: Go for the Warrior gear.
To explain it further, don't be tricked by the Death Knight's arsenal of spell effects, disease DoTs, and nukes. None of them use spellpower. It's completely useless. Instead, all of our spell-like damage works off of AP. The one exception comes off critical strike rating, as spells still appear to use spell critical strike rating instead of melee critical strike rating. Luckily, this isn't as much of a problem as it could be, since critical strike rating now applies to both spell and physical critical strike rating at once.
So what you're looking for primarily is Strength, which provides the customary 2 AP per hit, for your DPS. Agility will provide some nice melee critical strike rating and dodge, but is probably not as good as pure critical strike rating, which will provide critical strike potential for more Death Knight attacks. The devs have indicated that they make be willing to make Agility apply to spell critical strike for Death Knights if needed, so this may change, of course.
Death Knights do have one major difference from Warriors when it comes to tanking itemization: they can't use shields. That means, of course, that you don't want gear with shield block value or block rating stats. Strength will be rather important though, not just for gaining threat, but for conversion to parry rating. High armor and high parry seem to be the statistics of choice (besides the obvious) for the Death Knight tank.
It is, though, a bit difficult to properly guess what our final itemization will look like on tanking. Once we're 80 and we've seen what level 80 dungeon drops and first tier raiding gear looks like, we'll probably have a better idea of what to expect.
Weapon of Choice
The two choices open to Death Knights are dual wielding and 2-handers. I admit, I'm a 2 handed man all the way. It just feels right to me, especially since all the classic scourge Death Knights also use two-handers. I admit that I'm also pulled toward the need for less hit rating. In addition, many of the skills and talents of the Death Knight class are just biased toward the high damage of a 2-handed weapon. Still, there is a small but dedicated dual wielding Death Knight contingent out there, and there's a few solid dual wielding builds circulating, so it's probably here to stay in some capacity, even if that capacity is red-headed stepchild.
For 2-handers, the itemization is pretty straightforward. Get yourself a big slow 2-handed weapon with a high end damage so that you can take advantage of all the melee strikes and talent procs that work off weapon damage.
For dual wielding, you'll want a slow main hander for all the weapon damage strikes, but general consensus so far is that a faster offhander is best. Not only do none of the strikes thus far "hit with both weapons," but it means you're getting in more chances to proc talents such as Killing Machine, should you have them -- and many dual wielding builds do.
On Outland upgrading
Yes, you can get upgrades from Outland, even from Hellfire Peninsula. No, you don't have to take them. If you prefer form over function and plan to blast straight through Outland, you should be able to get away with keeping your blue gear til 70. If you do upgrade before Northrend, you will be in danger of looking like a clown, though, especially since the devs say they have no intention of itemizing for Death Knight specific gear sets before Northrend.
Still, if you're don't mind looking silly, there's some good upgrades to be had in Outland. Here's a few quest upgrades from Hellfire Peninsula, Nagrand, and Zangarmarsh:
Battlemaster's Breastplate: This breastplate out of Hellfire Peninsula is at the end of a long quest line for both Horde and Alliance, but it's a very nice upgrade from Saronite War Plate, with a good amount of extra AC and strength easily making up for the lost parry rating. It shows a lot of skin on most races though, even the males, so grab a tabard to cover it up.
Defender's Gauntlets or Suntrider's Gauntlets: Gained by a quest from either Falcon Watch or the Temple of Telhamat, these gauntlets have different names depending on your side, but the same stats. The upgrade from Bloodbane's Gauntlets of Command is much less apparent than it was with the breastplate, but it's a slight upgrade all the same, with a little bit of armor and a little bit of agility.
Studded Green Anklewraps: Yes, they're leather, but for pure DPS, they're a nice upgrade over Greaves of the Slaughter. You lose some critical strike rating, but 10 extra strength, some hit rating, some dodge rating, and some agility should take off the sting of that. You'll get them from the Cenarion Post.
Helboar Carving Blade: Yes, losing the Greatsword of the Ebon Blade sucks, but the carving blade here has better weapon damage and comparable stats. If you can bite the bullet, it's probably worth it. This is another reward from the Cenarion Post.
Bladefist's Breadth: From the quests to kill Arazzius at the Pools of Aggonar, this is a more than worthy DPS replacement for Signet of the Dark Brotherhood. Keep the signet around for tanking until you can find better.
Honed Voidaxe: The Ring of Blood in Nagrand is still an amazing chunk of XP and gold if you can get the group together for it, and the blue weapons it provides will take you right up to 70 with little difficulty. If you can get a group together for it, do so, as the voidaxe is an amazing upgrade.
Halaani Claymore: If you're lucky enough that your side controls Halaa a lot, this could be the perfect "congratulations for dinging 66" present for yourself. It's actually arguably a bit better than the Honed Voidaxe (especially for Humans), with a slightly higher top end damage and the critical strike rating which works on a wider variety of Death Knight abilities than the voidaxe's agility.
If you're planning to tank before Northrend, you can also pick up some stuff from quests such as Flintlocke's Piloting Pants and the Fearless Girdle, but you may be better off waiting for better stuff out of Northrend. Blacksmithing especially looks like it will offer some nice starter defense gear for the aspiring tank.
This is by no means a comprehensive list, though we may have one of those later, so as you level, keep a lookout for any other quest rewards that seem useful to you. Hopefully today's column has slightly demystified you to the world of Death Knight gear -- and hopefully it's not too obsolete by the time Beta's over and done! Happy gearing, and may your trip through Outland be quick and painless.