Death Knight: Unholy

Unholy is a fast, 2-handed weapon wielding DPS spec which deals large amounts of physical and shadow damage and uses a permanent ghoul pet. Unholy is quite versatile and brings various buffs and effects to a group, most notably Anti-Magic Zone, which can save groups. It also applies an 8% magic damage debuff (equivalent to Curse of the Elements or Earth and Moon) innately through Ebon Plague. It suffers from normal melee concerns such as roots and snares. As with all Death Knights, Unholy also provides the STR/AGI buff Horn of Winter.

Stats/Gearing:

Unholy Death Knights primarily look for Strength and Haste on their gear. The stat priority is as follows for both specs: 

Strength > Hit (to 8% cap) > Haste >Mastery> Expertise (to 781 cap)  > Crit  

A note on Unholy weapons: 

Looking at the talent tree, you may ask why you wouldn't want to put some points into Nerves of Cold Steel and dual-wield. The answer is a resounding No. There are many reasons for this- primarily that most of Unholy's damage comes from abilities that are based on main-hand weapon damage and there is no Threat of Thassarian equivalent in Unholy. The short version: Don't do it. 

Gems:

Bold Inferno Ruby, Fierce Ember Topaz, and Etched Demonseye are the gems you'll be wanting to use, depending on the slot color.

Runeforge:  

Rune of the Fallen Crusader 

Talents:

 The template spec is as follows:

Unholy Template Spec 

Note that the 1 point in Unholy Command is simply to progress through the tree and can be moved about as wanted/needed.

 Unholy Command: Taking this is mainly to NOT take Desecration to progress through the tree. See Desecration's description for reasons why you might take this. 

Desecration: Desecration is an AoE slow that gets tied to your main DPS nuke, which, in theory, sounds good, but can be annoying to tank around if slows are not required. The main issue with Desecration is that there's no "off" button for it, so if you need to not be slowing things down, you need to not be doing damage, if you've got the talent. Also, I'm personally not a fan of taking a talent to do something you can already do manually with Chains of Ice. 

 Once the template spec is completed, there's a few points left to spend. Here's a few good options:

Blood:

Improved Blood Tap: Allows more frequent usage of Blood Tap. I usually pass on this because I simply don't need extra runes that often, but it can be useful if something goes wrong with the rotation or if you suddenly need to use Chains of Ice or something. 

A note on Scarlet Fever: It looks good, but the debuff will be supplied by tanks and Scarlet Fever does NOT count as a disease for adding Scourge Strike damage.

Frost: 

Runic Power Mastery: Increases your RP cap. I recommend one point in this at maximum, because if you're using Death Coil as liberally as you should be, you won't go higher than 100. The one point is simply insurance. 

Unholy: 

Desecration: If you put one point into it before, making it a stronger slow won't hurt. 

Magic Suppression: More points in this means more RP sometimes. At 3/3, you take 0% magic damage while active, meaning you can stand in the proverbial fire and be rewarded for it with absurd amounts of RP. Just watch the duration on it. 

Anti-Magic Zone: If you put 3/3 in Magic Suppression, putting a point in this is an option. AMZ is a situationally useful move, but I personally like to have it just in case. 

Glyphs:

Prime: Death Coil, Scourge Strike, Raise Dead

Major: Anti-Magic Shell, Blood Boil, Pestilence

Minor:  Blood Tap, Death's Embrace, Horn of Winter

Rotation/Priority 

Unholy should be DPSing in Unholy Presence. 

 Single Target: 

>Apply diseases with Outbreak

>Death and Decay (yes, it's a DPS increase on single-target)

>Scourge Strike for primary DPS/rune use

> Festering Strike when 2x Blood+Frost runes are up for damage and to refresh diseases

> Death Coil when out of runes or on Sudden Doom proc

>Dark Transformation as soon as it's available

>Barring the above, toot your Horn of Winter

Multi-Target:

>Apply diseases with Outbreak

>Pestilence

>Death and Decay

>Use single-target rotation with occasional Pestilence.

Cooldowns   

Raise Dead: Not so much of a cooldown, this summons Unholy's permanent Ghoul pet. Make sure he stays alive, or at least, gets brought back to life with this if he goes down.  
Unholy Frenzy: This is a potent cooldown that will massively increase your DPS. Take note that it IS an enrage effect, and the only thing you'd ever want to cast it on besides yourself would be a Fury Warrior- they'd benefit a lot more from it. Note that you will reach/exceed haste cap if you combine this with Bloodlust, so try to use it before or after, not during. 
Summon Gargoyle: The Gargoyle will fly around bombarding the target with Nature damage and will otherwise follow the same commands you send to the Ghoul. It's important to note that as a temporary pet, the Gargoyle will inherit your current stats, so it's generally a good idea to summon him during either Unholy Frenzy or Bloodlust to maximize his damage.

Army of the Dead: This will either massively increase your DPS or wipe your group. Army ghouls, unlike the one from Raise Dead, will taunt anything they attack. If something needs to be moved in a specific manner or needs to be targeting the tank, Army will fuck it up, hard. Make sure a fight is safe to use Army on before using it.   

Raise Ally: Our new Battle Res. Pool up some RP to cast it on an ally for an instant res- making this the best battle res in the game. Having said that, knowing who to cast it on is rather important- when faced with a choice, it's always best to bring up another player with a battle-res. Having said that, the usage will vary wildly depending on what's going on- communicate with your group.

That's about it for Unholy Death Knights. This post will be updated as patches come and go and as more information is made available to me.