StarCraft/Terran units

The building in parenthesis following the unit name is where you prodcure the units from

Terran
SCV (Command Center) This is the basic resource gathering unit/construction unit for the Terrans. They're produced at Command Center for 50 minerals each. Typically in a game with a regular size patch of minerals you'll want to have about 30 of these guys -- with more if you've got expansions or more than the usual amount of minerals. For Vespene geysers, have as many as it takes so that there's one and only one SCV waiting at the refinery for the one already in to come out with a full load.

Marine (Barracks) Marines for the basic unit for the Terrans, they're reasonably powerful as well. They can be bunkered for additional protection (and they make a very good defense if they are bunkered). A combination of Medics and Marines can spell death for a Zerg opponent if they are not adequatly prepared for it. Marines never go out of style and you should have a healthy supply of Marines to assist your heavy duty war machines, or to mop up enemy forces.

Firebat (Barracks) Like Marines, the Firebat is an infantry unit. The difference is Firebats have more armour, less range, but do "splash damage". Teamed with some marines they can pulvarize Zerglings, or take a chunk out of Zealots armour. Firebats become less useful later in the game because they need to be close combat, and they cannot hit air units. Firebats require an Academy to be built.

Ghost (Barracks) The Ghost is an infantry unit, however a Ghost is more akin to a spellcasting unit than a combat unit. Typically ghosts will be used for their "target nuke" ability, or to lock-down enemy units (especially Protoss Carriers, or other Terran Siege tanks). Ghosts also have the ability to "cloak". Ghosts require an Academy, and a Science Facility with Covert Ops to build. Ghosts require 50 gas but only 25 ore, so they are useful in a low-ore game. They also have the longest range of any ground unit, although they fire slowly.

Medic (Barracks) (Brood War Only) The Medic is a unit added in the Broodwar expansion pack, and is introduced to the Koprulu Sector by the UED's armies. The Medic will automatically heal damaged infantry (as well as SCVs, and Protoss infantry/Zerg units if they are allied with you.). They increase the effectivness of infantry drastically. Medics require an Academy to be built.

Vulture (Factory) The Vulture is available once a Factory is built. Its a fast unit with a powerful (but slow) attack. Vultures are effective at taking out enemy Zealots, if you're prepared to "Micro Manage" them in combat. The "Spider Mines" upgrade adds a lot of value to the Vulture, as you can plant mines on the battlefield to help you keep tabs on the enemy's movements, as well as thin their numbers a little bit. Plus the mines put Vultures sort of on the level with Protoss Dragoons, who can be a nightmare for a fledgling Terran colony. Vultures cannot target air units. Siege Tank (Factory) The Siege Tank is available at the factory when a machine shop add-on has been built. These are the Terran's heavy artillery (either the Dominion or the UED). There are a number of Terran strategies that incorporate these wonderful seige engines. Once you've researched their "Seige mode" upgrade, a Seige Tank can sacrifice it's movement to gain a large boost to damage and range. At a later time the tank can be taken out of seige mode and repositioned. These babies are great for offense and defence. Seige tanks cannot target air units.

Goliath (Factory) The Goliath is an ground-to-air missile launching vehicle. It can also target ground units with it's side cannons. Its a very useful combat unit, and in some cases can save your life. Besides Marines, it's the only unit that can target air before the Starport comes online.

Dropship (Starport) The Dropship is used to ferry troops around. Its a very important unit. Typically they are used to either populate the world on "Island Maps" or to place troops in more favourable positions (Like placing Seige Tanks on a ledge, where they can rain death upon the enemy).

Wraith (Starport) The Wraith is a fast airborne combat vehicle. It is capable of attacking both air and ground units. It also has the ability to cloak. These are useful in groups of about 6-12 (more is excessive, they rely more on suprise than strength, too many ruins the suprise element). Typically they're used to pester outlying enemy installations or fortifications. However, watch out, if the enemy brings a "detector" the Wraiths will be revealed, and since Wraiths, like Trabants seem to be made out of cardboard, destroyed quickly.

Valkyrie (Starport) (Brood Wars Only) The Valkyrie is an air-to-air unit. Its not all that popular (I would have preferred a nice bomber =) but its got some use. Typically you build them when your expecting a large fleet of air units coming your way. Valkyries do splash damage and can quickly anihillate groups of air units.

Battle Cruiser (Starport) The Battlecruiser is the Terrans most powerful unit. Its also the most powerful unit in the game (when it has its Yamato Gun upgrade...). Its a competant fighter, but a single Battlecruiser isn't going to win the game for you. 12 or so can be a fleet of death if you've already got a lead and if handled right can likely win the game for you. In more even matches, BC's are sometimes used to harass the enemy with their long range Yamato Cannon. Simply target the enemy unit you'd like to die, then fire, then retreat and repair BC. Rinse. Repeat. They are excellect for killing Terran missle turrets to enable penetration by cloaked units.

Science Vessel (Starport) The Science Vessel is the Terrans' other spellcasting unit. It has a few spells that are useful. Defensive Shield can be used to bolster a units hp up (it adds ~200 temporary hp). Irradiate damages living organisms, so it can be cast on Zerg swarms to weaken a cluster of them (try casting on a group of bunched up gardians, and watch them suffer, or cast it on your seige tank. The tank won't take damage, but Zerglings that are attacking your tank will.) The other spell, EMP, takes away all the energy (spellcasting points) from units, and all the Protoss shields. So a well cast EMP shockwave essentially halfs the Protoss units hitpoints. It will also cause Wraiths and Ghosts to decloak.

Protoss
Zealot (Gateway) ground unit, a Zealot channels his enormous psychic powers into creating a plasma shield and energy blades for offensive and defensive purposes. The Zealot is excellent at hand-to-hand combat, and can take a lot of pounding. Can't attack air targets.

Dragoon: (Gateway) A Zealot, after becoming mortally wounded, can volunteer to have its brain placed inside a robotic exoskeleton, and becomes a Dragoon. The Dragoon shoots bolts of antimatter at ground and air targets, and moves moderately quickly.

Scout (Stargate) a light aircraft, the Scout has twin guns under its wings and a pair of missile launchers. Used in packs they are deadly.

Carrier (Stargate) Heavily armored flying machines, they manufacture robotic Interceptors to attack targets. Carriers can hold 8 Interceptors, and are very nasty if used in numbers.

Interceptors (Carrier) Small robotic fighters with limited range which are spawned from Carriers. They fly randomly and then all rush the target at once and shoot it and disperse. Can easily confuse an enemy as to which one to hit, and seeing tons of these things flying around can have a noticable phsycological impact on a human opponent.

Reaver (Robotics Facility) the Protoss equivalent of a Seige Tank, the Reaver shoots robots called Scarabs from its insides, which contain antimatter for a devastating blast. Downside: They move excruciatingly slowly and can't attack air targets.

Shuttle (Robotics Facility) As it's name implies, the Shuttle ferries other units by air around the map.

Observer (Robotics Facility) The Observer is a permanently cloaked air unit which can do nothing but move around and spy on the board. These are very usefull for putting in unclaimed resource areas or other strategic areas (Mountain passes, enemy perimeters) to keep tabs on the board.

Arbiter: (Stargate) Spell-caster, an Arbiter casts a cloaking field on groups of units underneath it. Stasis Field, and Recall for spells. You can't cloak an Arbiter with another one, unfortunately.

Corsair (Stargate) (Brood Wars Only) Attacks only Air targets w/small neutron pulses. Can also deploy Disruption Webs, which prevent ground units under the web from attacking. Used mostly for disabling enemy tanks and defensive structures, (with D-web) and hunting Zerg Overlords. Medium unit.

High Templar (Gateway) spell-caster: doesn't attack directly, sort of lousy except for Psionic Storm. Merges into Archon.

Archon (Merge 2 High Templars) Needs 2 HT. Fires huge bolts of psychic energy from hands, enormously powerful. Ownly downside is it's hit points are almost totally sheilds, so if it is hit with a few too many EMP blasts, an SCV might be able to take it out.

Dark Templar (Gateway) Assasins, they are endowed w/permanent cloak. They have enormous attack damage, yet little shields/HP. Use for suprise attacks. They can merge into a Dark Archon.

Dark Archon (Merge 2 Dark Templars) (Brood Wars Only) Needs 2 DT. is a spell-caster, and can mind control other units. Very useful. Mind control is best excersized against a builder unit of an enemy of a different race so you can build all their buildings and get in on their technology.

Zerg
Zergling (Hatchery) nasty, little buggers. Designed to be melee units, and can be bred two at a shot from a larva. Used in enormous numbers, they can damn near wipe out everything as long as they aren't killed first. 'Lings' are a common nickname for these, and 'cracklings' refer to their most upgraded form. (+speed, + attack speed, +3 attack and +3 defense)
 * Any aircraft can kill them easily, as they can't attack air targets. ALso use marines in bunkers, a lot of zealots, or more zerglings to counter zerglings.
 * Common Strategies --- 4 or 6 ling rush in the first 1 or 2 minutes of a game, Muta-ling rush within the first 5 minutes of the game, and commonly used with Defilers and Ultralisks. These stronger units, if used correctly, will act as a sponge and allow these Zerglings enough time to cause some damage.

Hydralisks (Hatchery) These things spit hyper-velocity, super-dense darts at you, ripping you to pieces. Used in great numbers, they can annihilate everything (both ground and air).
 * These are your general "mob" monsters. They can handle everything as they are not specialists in any kind of way. Be wary of the general mob-killers such as Tanks, Reavers, and even High Templar.

Drone (Hatchery) a worker-unit, like the SCV. Can burrow, but just kill them like you would an SCV.

Mutalisk (Hatchery) a 'small' flying creature, the Mutalisk shoots a worm at you that ricochets and hits other targets. Does little damage, but used in 12 or more its nasty.
 * Pair these up always with Zerglings, and the pair can counter nearly all enemies.

Ultralisk (Hatchery) super-behemoths, almost worse than Siege Tanks. To me, they've always looked like a super-Zergling, 20 ft. tall w/huge blades on their arms. These things will kill anything ground; but, like the Zergling, they can't fight air targets.
 * Ironically, while these things are armored to the core, Zerglings easily outdamage them in damage/second. Pair these babies up with Zerglings, and you can break any ground defense there is.

Guardian (Hatchery) the Mutalisk can mutate into the armored, long-range Guardian. The Guardian can't atack air targets, and can only shoot at the ground.
 * Use these as snipers, as Guardians have the longest non-magical air-to-ground attack in the game. By non-magical, I mean excluding Yomato Cannon, and etc.

Scourge (Hatchery) suicide units, they fly into structures and rip them to pieces. No weapons, little armor, only suicide.
 * These are best used as a surprise attack. Few people expect 12 Scourges to rip apart their entire air fleet.

Defiler (Hatchery) spell-caster; casts plague, dark swarm, they're nasty buggers. Lucky they don't have any conventional weapons, so they're easy to kill. The question is finding them first. USE DETECTORS!
 * Plague is one of the most useful attacks in the game. It is basically poison in any RPG, every half a second or so, 3 hp is drained away.
 * Dark Swarm is THE most nasty spell in the game. While this dark cloud looks harmless, it will make all units under it invincible to ranged attack. This means units under a dark cloud are invincible to ALL air units, Marines, Goliaths, Tanks, Vultures, Ghosts, Dragoons, Archons, and Hydralisks . Unfortunately, Dark Swarm works for both Friend and Foe, so use only when you don't got Hydralisks. Note: Archons and Tanks will still damage units because of splash damage. However, the initial 30 or 70 attack that hits the target will be nullified to 0.

Queen (Hatchery) a flying spell-caster. Nasty, but easy to defend against. Ensnare, Spawn Broodling, Infest Command Center, and Parasite for spells.
 * Spawn Broodling is an instant kill for all non-robotic ground units. (Dark) Archons and Reavers are the only "robots" in the game.

Infested Terran (Hatchery) Once a Queen has infested a sufficiently damaged Terran Command Center w/toxins, the people inside are enaslaved and genetically modified into explosive suicide ground units. They run up to their target(s) and explode, causing horrendous damage in game statistics. Easy to shoot them down w/air units.
 * Their attack is an amazing 500 (that is as much as a Terran Nuke!). These are rarely used however, as they are very very weak, and rarely reach their target.

Devourer (Hatchery) (Brood Wars Only) Slowest attacking unit in the game. Launches acid at the enemies, that deteriorates armor. They are only air-to-air units. The acid goes upto -9 armor.
 * Its not the Devourer itself that is so powerful, but the acid that comes with it that kills. Never send Devourers on their own, they will be ripped to shreads even by the weakest of air units. Mutalisks and Hydralisks pair well with these, as every time a Devourer attacks, Mutalisks can armor break more and more.

Lurker (Hatchery) (Brood Wars Only) Underground, stealthy, and deadly. Mass damaging and mass killing machines.