Death Knight - Frost DPS

Purpose

Death Knight frost DPS is, by Blizzard's design, the dual-wield tree. Blizzard has designed this tree around encompassing the dual wield playstyle, and - as of 3.3 - it is the farthest behind the other trees in terms of both utility and damage. The only real reason to play in this tree (aside from liking its playstyle, which - if it's okay with your raid - is a perfectly legitimate reason; it's a fun build) is if your raid does not have an enhancement shaman and desperately needs the melee haste buff that a Frost DPS DK with Improved Icy Talons can provide in their place.

Two-handed frost for DPS is not a build that Blizzard is encouraging or supporting at this time, and is, for all intents and purposes, a dead spec. Two-handed weapon wielders will want to look at the Blood or Unholy trees, instead.

Key Talents

Nerves of Cold Steel∞ - Increases your chance to hit with one-handed melee weapons by 3% and increases the damage done by your off-hand weapon by 15%. This is one of the talents that makes Dual Wielding viable. This talent is also why dual-wielding DKs need somewhat less hit rating than the other two trees.
Threat of Thassarian∞ - This is the other magical dual-wield talent; Threat of Thassarian allows you to actually hit with your offhand on all your strikes. Without this, you are gimping yourself severely.
Howling Blast∞ - An AoE that effects all enemies within 10 yards of the target with frost damage. Not quite the cornerstone of the class like it used to be, but still powerful, and you'll be throwing off free ones thanks to Rime.
Killing Machine∞ - This procs off melee attacks and causes the Death Knight's next Icy Touch, Howling Blast, or Frost Strike to be an automatic critical hit (if it hits - it can still miss). This is often used in conjunction with Howling Blast or Frost Strike (usually the latter).
Improved Icy Talons∞ - Provides a 5% haste increase on the DK at all times as well as a 20% melee haste increase to all party/raid members for 20 seconds after casting Icy Touch. As of 3.3, this is the only reason to bring dual-wield Frost DKs to a raid.
Rime∞ - This procs off of Icy Touch and causes your next Howling Blast to use no runes. Additionally, your Icy Touch and Obliterate have a +15% chance of a critical hit at all times.
Frost Strike∞ - Frost tree's signature strike. Unlike Unholy and Heart Strikes, Frost Strike runs off of runic power, and will be your primary runic power dump (as opposed to the other two builds, which use Death Coil).
Unbreakable Armor∞ - While it's not included in some Frost DPS builds, and is usually considered a tanking talent, Unbreakable Armor does provide a large strength boost while it's up, and is therefore the closest thing Frost has to a DPS cooldown.
Deathchill∞ - Also not included in some Frost DPS builds, but if you do, it simply gives you an automatic crit with an Icy Touch, Frost Strike, Howling Blast, or Obliterate. Usually best used with Obliterate, since it is the only one that is not included on Killing Machine.

Talent Spec, Glyphs, Sigils, and Runeforges

There are three general talent specs for Frost DPS.

0/54/17∞ - Cookie-cutter Frost DPS spec. Picks up every important talent.
3/53/15∞ - The previous spec, modified to take care of threat problems.
15/54/2∞ - Situational AOE spec, best for fights like Anub'arak, Freya, or Mimiron where multiple targets will be up most of the time.

The only major glyphs worth using are Frost Strike, Obliterate, and Icy Touch; the only minors, Raise Dead, Pestilence, and Horn of Winter.

As for Sigils, it's a close running between Sigil of Virulence and Sigil of the Hanged Man. Hanged Man will probably be better in ICC, but there may be movement-heavy fights (Gunship, etc.) where you are unable to keep its stacking buff up, in which case Virulence pulls ahead. If you can't get either of those, Sigil of Awareness is a very acceptable (and close) third place, and may even be better in some situations.

Attack Priority

Frost really has nothing in the way of major cooldowns (ala Blood's Dancing Rune Weapon or Unholy's Summon Gargoyle), so your rotation will pretty much never change.

Frost does not have a simple rotation. If you want a rotation you can apply by facerolling, this is not the spec for you. Frost operates on a priority system; at any given time, you do what is highest on your priority list. The list, from highest to lowest, looks like this:

Single Target

Using a Killing Machine proc with Frost Strike.
Using a Killing Machine proc with a Rime proc.
Keep Frost Fever up - Icy Touch.
Keep Blood Plague up - Plague Strike.
Obliterate
Blood Strike
Frost Strike
Rime
Horn of Winter

AOE

Howling Blast (including Rime procs)
Keep Frost Fever up - Icy Touch
Keep Blood Plague up - Plague Strike
Pestilence
Death and Decay
Obliterate
Blood Boil
Frost Strike
Horn of Winter

Weapon Choice

This cannot be stressed enough - the days of Frost using fast weapons is over. You want a slow main hand weapon, and a slow off-hand weapon.

Stats (In Order of Importance)

Hit rating - 164 with Nerves of Cold Steel, 263 without. This gets you to 8% total, the cap for special attacks.
Strength - this is essentially your biggest DPS gain at any given time once you're hit capped, so if you can stack Strength, do so.
Expertise - you need 26 Expertise (not expertise rating) to reach the Expertise cap; 5 of this is given to you for free by Tundra Stalker, so you only need 21. This works out to 172.2 expertise rating. Humans using a sword or a mace only need 147 expertise rating; dwarves using maces or orcs using axes only need 131.2 expertise rating. This is not as important before getting hit capped, but it is a good thing to pursue once you are.
Crit - very important to Frost, as its death knights tend to have high crit multipliers.
Armor penetration - more useful to Frost for single-target fights than any others, due to the high amount of Obliterates used. However, while it is useful, it should not be stacked to excess.
Haste - more useful to Frost than the other two trees due to our naturally slow weapons, but not worth skipping expertise, strength, crit, or armor pen for.
Attack power - less useful than the other stats because we don't have anything that scales with it. If you have a choice between AP or Strength, always choose Strength.
Agility - you will, more often than not, have this on your weapons, because almost all the one-handed weapons are itemized for either (1) tanks or (2) rogues, and you should not be using tank weapons to DPS. Agility is a decent stat; for DKs, it essentially converts to crit (and will be a small AP boost for frost DKs using the AOE-specific Frost build, due to Bladed Armor).
Armor - most builds don't include Bladed Armor, but for the one that does, Plate is slightly more attractive than Mail simply because of the increased armor converting to increased AP.

Recommended Enchants

Head - Arcanum of Torment (Ebon Blade)
Shoulder - Master's Inscription of the Axe (Inscription), Greater Inscription of the Axe (Sons of Hodir)
Cloak - Greater Speed
Chest - Powerful Stats
Bracers - Greater Assault
Main Hand - Rune of the Fallen Crusader
Off-Hand - Rune of the Fallen Crusader, Rune of Razorice (Razorice is predominantly better on the offhand than Fallen Crusader, except for movement-heavy fights where you can't apply the entire debuff stack or it falls off)
Gloves - Crusher, Hyperspeed Accelerators (Engineering)
Belt - Eternal Belt Buckle
Legs - Icescale Leg Armor
Boots - Cat's Swiftness, Greater Assault, Icewalker, Nitro Boosts (Engineering)
Rings - Assault (Enchanting)

Gems

Red socket: Bold Cardinal Ruby (+Str)
Yellow socket: Inscribed Ametrine (+Crit/+Str)
Prismatic socket: Nightmare Tear (+10 all, unique-equipped)
Meta gem: Relentless Earthsiege Diamond (used over Chaotic Skyflare Diamond due to not having to use useless [for DPS] blue gems)

Your gemming strategy should look like this.
Do I have a meta gem? If not, put a Relentless Earthsiege Diamond in your helmet.
Are my meta gem requirements met? If not, put a Nightmare Tear in some socket - preferably a blue one on a piece that gives a strength bonus. Voila, your meta gem requirements are met.
Do I have prismatic sockets (blacksmithing sockets, belt buckle, etc.)? If so, put a Bold Cardinal Ruby into them.
Do I have a piece that gives Strength bonuses and uses only red and yellow sockets, or a blue socket that I can put a Nightmare Tear in? Put Bold Cardinal Ruby into the red sockets, and Inscribed Ametrine into the yellow sockets. STRENGTH IS THE ONLY SOCKET BONUS WORTH WORRYING ABOUT.
Do I have any sockets remaining? Socket a Bold Cardinal Ruby.

Recommended Consumables

Flask of Endless Rage (counts as a Battle and Guardian Elixir)
Elixir of Mighty Strength (Battle Elixir)
Foods that provide Strength, Attack Power, Hit (if not capped), expertise (if not capped) or a combination of as many as possible. There are several food options.