Thanks to Omega for this idea. Visit the other two tactical guides:
-The Protoss Tactical Guide by Knee of Justice
-The Terran Tactical Guide by Omega
Also thanks to Knee for the solid feedback and help on this. Enjoy ^^

NOTICE: This is a GUIDE and is expected to be used as such. It is meant to be a helpful tool when looking up strategies associated with certain units, NOT to give a detailed description of each unit's stats. Like an Encyclopedia, dont bother trying to read the entire thing, but instead, use it to investigate certain units individually.

With Beta around the corner, we thought it would be interesting to have a Strategy guide for the different races in SC2. This guide is not meant to replace the official Starcraft 2 Armory Guide, but rather, augment it by providing unit strategies, combos and roles down in one central location. This will help organize discussions when beta comes out as any new strategies and so forth can be posted to this guide so that all may have access to the new ideas and unit combinations being developed in SC2. Perhaps when Beta actually comes out, this may become a sort of Beginners guide to the units, strategies and micro/macro tactics being adopted in SC2.

Burrow Mechanic:

Burrow requires an upgrade from the Lair/Hive. While a unit is burrowed, it is invisble to your enemies unless they bring a detector to the burrowed unit (or scans if Terran). Burrowing has come far since SC1 and now is a must have for some units:
-Ultralisks have acquired the burrow ability in SC2
-The Infestor and Roach both have the ability to move while burrowed
-The Lurker burrows slow because it attacks only underground
-Roaches only regenerate fast underground

Burrow has been moved to Lair tech as of Blizzcon 09.

Nydus Worm Mechanic:

Nydus Worm:

Currently, the Nydus Worm may be spawned to patches of creep on the map. The Nydus Worm morphs in as if it was a building. Units may be stored inside the Nydus Worm and unloaded at other Nydus Worms/Networks.

This is how the Nydus Network works:

1. Nydus Network is built by the Drone at Lair tech.
2. Units are loaded into the Nydus Worm.
3. The Nydus Worm may be spawned on creep for 100 minerals each and takes 5-10 seconds.
4. Units can then enter a Nydus Worm or Nydus Network and exit through any other Nydus Worm or Nydus Network.
5. If there is at least one other Nydus Worm on the map and you are morphing in a Nydus Worm that gets killed, the units inside the Nydus Network will not be killed.

To sum things up, the Nydus Network is basically just the Nydus Canal except you can travel between any number of points instead of just two.

Changeling Mechanic:

The Spawn Changeling is an ability that comes from the Overseer. When the Changeling comes in range of the foe, it changes into that race's first tier unit (ex: Marine, Zealot, Zergling). Once the Changeling has changed shape, it will not appear as an enemy to your foe. Your foe will have to manually target the Changeling themselves if they spot it.

The Changeling in action: 1:15-3:30 sorry about the bad quality.

Unit Strategy Guide:

NOTE: Detailed Unit Statistics may be found here:
Zerg Game Guide

Drone:

Minerals: 50
Vespene: 0
Health: 40
Damage: 5
Abilities: Gather, Morph to structure, Burrow

Strengths: Able to morph into any Zerg structure, can gather resources.
Counters: Nothing.
Weaknesses: Always the fiirst target for base raids.
Countered by: Colossus, Stalker, Viking, Reaper.

The Drone is the least efficient worker of the three races. The Drone is lost when making the building. Luckily, the new Queen's mechanic makes up for this. Drones can also burrow if a base raid takes place.

Overlord:

Minerals:100
Vespene: 0
Health: 200
Damage: 0
Abilities: Overseer Mutation, Transport, Excrete Creep

Strengths: Spawns Creep, transports units.
Counters: Nothing.
Weaknesses: Slow, suceptible to anti-air, requires mutation for detection.
Countered by: Viking, Phoenix, Corruptor.

The Overlord is not a detector! It has gained a few other abilities though.

Transport and Speed are researched together at the Lair. 2 for 1 deal.

The Overlord now has the ability to spread Creep, making it much more essential to use than just transport and supply. The Overlord will be the best thing to have around once your Nydus Network finishes though, so don't upgrade all of them to Overseer. Also, don't let them wander too far without protection. There will be hungry AtA units by the time you need an Overlord for your Nydus Worms.

Excrete Creep

Overseer:

Minerals: 50
Vespene: 100
Health: 200
Damage: 0
Abilities: Spawn Changeling, Detection, Spore Cloud

Strengths: Faster, Designated Detector.
Counters: Nothing.
Weaknesses: Suceptible to anti-air, loses abilities after mutation
Countered by: Viking, Phoenix, Corruptor.

The Overseer is now the new designated Zerg detector. It will be smart to always keep one handy for Dark Templars or Ghosts. This means that you will need to have a fair balance between your Overlords and Overseers. The Overseer's vision increases the longer it is left idle. Overlords won't be required for the Zerg because it depends on what build you will be using.

The Spawn Changeling mechanic can be found earlier in this thread.

The Spore Cloud ability a line of sight blocker which your foe cannot see past (only with air units). This ability will be most useful with range units such as the Hydralisk or Brood Lord. The Mutalisk I cannot see working well with this ability because it only has 3 range.

Queen:

Minerals: 100
Vespene: 0
Health: 175
Damage: 4x2
Abilities: Burrow, Transfusion, Spawn Creep Tumor, Spawn Larva

Strengths: Excelent base defence, economic boost.
Counters: Light units and base raiders.
Weaknesses: Slow, big target for base raiders.
Countered by: Battle Cruiser, Thor, Void Ray.

The Queen's main ability is Spawn Larva. This ability adds 4 extra larva to the Hatchary. This is not jsut an economic boost for you, but also a faster way to pump out an army. This ability costs only 25 energy and takes 40 seconds so having a couple Hatcheries at your base would do good if you took about a 20 second interval between each Hatchery to begin spawning more larva.

This is where having more than one Queen is useful. Transfusion is basically a mix between Repair and Heal. It instantly heals 200 health of a selected unit/structure. This is probably best used on either on a critically damaged Hatchery, Nydus Network, or Spine/Spore Crawler. Ultralisks wouldn't be so bad either.

The Creep Tumor ability extends the Creep. This ability can be used offensively because Zerg travel 30% faster on the Creep. This will help the Zerg out much more with their micro.

Spawn Larva

Zergling:

Minerals: 50
Vespene: 0
Health: 35
Damage: 5
Abilities: Burrow, Baneling Mutation.

Strengths: Open areas, Fast, Small, 2 Zerglings per egg, ability to select any amount of units at once.
Counters: Immortal, Stalker, Marine, Thor, Colossus.
Weaknesses: Choke points, Splash attacks, the new clumping system.
Countered by: Disruptor, Marine, Reaper, Hellion.

Zerglings have barely changed from the first Starcraft. It's conventient to have a very massable unit with a morph ability. Aside from that, the ability to select any amount of units at once will do wonders for macroing with Zergling. The downside to this is that units bunch together now, making Zerglings much more suceptible to the Siege tank and other spalsh attacks. The new pathing system also makes Zerglings much more agressive in the heat of battle because they surrond their enemy much more easily now.

Baneling:

Minerals: 50
Vespene: 25
Health: 30
Damage: 15 (+20 vs light)
Abilities: Burrow, Attack Buildings, Detonate.

Strengths: High Damage, no friendly fire, detonate button.
Counters: Marine.
Weaknesses: Suicidal attack, slow without speed upgrade.
Countered by: Hellion, Siege Tank.

The Zerg Baneling is a first tier unit replacement for the old Infested Terran. It's high damage out-put plus splash affect other first tier units drastically. Burrow and the detonate button are a tough combo that will force your opponent to be over cautionous to where they steps on your territory. The Banelings are also very accessible because it mutates from the Zergling which is a very massable unit.

Baneling sneak attack: 4:50-5:00

Roach:

Minerals: 100
Vespene: 0
Health: 160
Damage: 8 (+8 vs biological)
Abilities: Burrow, Fast Regenerate

Strengths: Health restores fast underground, good vs biological units.
Counters: Zealot, Marine, Reaper, Hellion.
Weaknesses: Focus fire.
Countered by: Stalker, Immortal, Archon, Marauder, Siege Tank, Thor.

The Roach is the Zerg's tank. If used right, the Roach can absorb huge amounts of damage because it's health regenerates fast. This ability is a must have with Burrow because the Roach may regenerate only underground. If your opponent knows what he is doing, he will focus fire and wear each one down one by one. Be sure to always bring along some Zerglings or Hydralisks.

The Commando Roach: 10:30-10:58

Hydralisk:

Minerals: 75
Vespene: 25
Health: 80
Damage: 8 (+4 vs armored)
Abilities: Lurker Mutation, Burrow

Strengths: Good anti-air.
Counters: Phoenix, Void Ray, Mothership, Banshee, Battle Cruiser.
Weaknesses: Expensive.
Countered by: Reaper, Hellion, Siege Tank, Thor, Viking.

The Hydralisk has been made back into the old massable type from SC1 as of Blizzcon 09. Though they are Lair tech, they are extremely useful in almost any situation. The Hydralisk id your ideal backbone unit and supports any unit.

Lurker:

Minerals: 50
Vespene: 100
Health: 125
Damage: 15 (+15 vs armored)
Abilities: Burrow (no upgrade required)

Strengths: Attacks underground while invisible, siege range (after upgrade).
Counters: Stalker, Hellion, Marauder, Roach.
Weaknesses: Low health for Hive tech, slow burrow, detectors.
Countered by: Immortal, Marauder, Siege Tank.

The Lurker is now Hive tech in SC2. This is probably because of their strong attack vs. armored units and their long range upgrade. This will be a very useful unit to have on cliffs and countless other positions (mostly chokes). The Lurker automatically recieves the Burrow ability, reguardless of whether it has been researched or not.

Mutalisk:

Minerals: 100
Vespene: 100
Health: 120
Damage: 10
Abilities: Multiple Target Attack

Strengths: Great for harrasing, fast.
Counters: Colossus, Mothership, Marine, Banshee,
Weaknesses: Short range, suceptible to splash damage.
Countered by: Stalker, Thor, Viking, Battle Cruiser.

Nothing about the Mutalisk has changed much except for the fact that it does not mutate into anything now. This gives the Zerg's backbone air unit the freedom of it being it's own unit and not having to decide between AtA or AtG. The Mutalisk is best to have around in any situation for ground or air support. Mutalisk stacking is going to be even more effective due to the unlimited selection mechanic. They will not have to be controlled in seperate groups anymore.

Corruptor:

Minerals: 100
Vespene: 75
Health: 180
Damage: 18
Abilities: Brood Lord Mutation, Corrupt.

Strengths: Strong AtA, Corrupt units attack the enemy for a time.
Counters: Void Ray, Banshee, Battle Cruiser.
Weaknesses: GtA units, light AtA units.
Countered by: Marine, Thor, Phoenix.

The Corruptor is a very strong AtA unit. When enemies are 'killed', they become an immonile turret that fires upon the enemies air units. The immobile turret has a range of 6 and a damage of 7. Be sure to bring Hydralisks in case you run into Vkings or Phoenixes because light air units will take Corruptors down in a flash. Best used as a counter late game to Motherships, Carriers, or Battle Cruisers. Also, Corruptors come in pretty handy if you run into ground units because they can morph into Brood Lords.

Brood Lord:

Minerals: 100
Vespene: 100
Health: 275
Damage: 25
Abilities: Spawn Mantalings

Strengths: Spawns two Mantalings every attack, strong AtG
Counters: Archon, Ghost.
Weaknesses: AtA units, massable GtA units.
Countered by: Corruptor, Phoenix, Viking.

The Brood Lord is a mutation from the Corruptor. They have a powerful AtG attack that spawns 2 Mantalings upon each hit. Even though these Mantalings are weak and have a timer to their life, they create a great distracton and allow the Brood Lord to keep attacking. This unit is great for harrasing the enemy while prepare for an attack. Be sure to bring anti-air when using these powerful flyers.

Infestor:

Minerals: 100
Vespene: 200
Health: 120
Damage: 0
Abilities: Burrow, Plauge, Neural Parasite, Spawn Infested Terrans

Strengths: Moves underground, fast anti-air back-up.
Counters: Any unit with high damage or special abilities.
Weaknesses: No attack.
Countered by: Detectors.

Sporting a nifty new design, the Infestor is a unique Zerg caster with the ability to move while burrowed.

Everyone should know what Plauge is because it is an old ability from the Defiler in SC1. The ability spreads over a wide area of effect and causes all caught within, to start dropping health. The health stops going down after it hits 1hp. This makes the perfect support if you are not prepared for a Marine attack on your base. The Spine Cralwers can finish them off.

Neural Parasite is a temporal version of SC1's Mind Control, owned by the Dark Archon. It takes control of an enemy unit for 10 seconds. This would be best used when your enemy unleashes a tide-turning unit on you.

Neural Parasite: 7:35-8:00

Spawn Infested Terran: 4:30-4:50

Infested Terran:

Spawn Infested Terran is the perfect choice if you need fast anti-air support. Leave an Infestor lying around your base incase this happens.

Ultralisk:

Minerals: 300
Vespene: 200
Health: 600
Damage: 20 units, 60 structures
Abilities: Burrow

Strengths: Chokes, high damage and health.
Counters: Archon, Marine, Ghost, Hellion, Ultralisk, Thor.
Weaknesses: Open areas, large target, expensive.
Countered by: Any AtG unit, Immortal, Void Ray, Marauder.

The Ultralisk is more bad ass than ever with Burrow as an ability. This calls for some serious ambushes. The Ultralisk does have the Chitinous Carapace upgrade anymore because it comes default with 3 armor. It is also much more powerful and huger than ever. This is the best unit to bring with you if you want to raze an expansion. Supported by Zerglings, the dynamic combo will be harder to penetrate then ever.

I will update this thread as necessary and when I have time.