Starcraft 2 is coming, going to be released on July 27, 2010!!!!

Starcraft 2 will be split into three separate products, based around the terran, zerg and protoss campaigns respectively. The first will be called Terrans: Wings of Liberty, the second will be called Zerg: Heart of the Swarm and the third will be called Protoss: Legacy of the Void. The latter two products are considered to be expansion sets. Little to no work is currently being done on them, Wings of Liberty being Blizzard's focus.
Blizzard Entertainment chose this route due to the challenges they faced creating the campaigns. Now they can create more content per campaign, such as movies, sets, props, characters, missions (including Easter egg missions) and so forth. Each character will have their own arcs, missions and dialog.
Each campaign will have 26-30 missions in total (including branching missions) and a set ending, rather than a cliff-hanger.
All three races will be completely developed for the multiplayer skirmish mode.
The three campaigns do not occur simultaneously in-universe. Rather, they occur in chronological order, each campaign beginning immediately after its predecessor.
The latter two expansions are expected to take over a year to release. Each will upgrade and expand multiplayer content in addition to containing a campaign, such as new units, abilities and structures.

By: http://starcraft.wikia.com

The terrans are relative newcomers to the Koprulu sector. They are the descendents of a disastrous colonization expedition launched from Earth centuries ago, its human cargo made up of dissidents and malcontents the government deemed expendable. The survivors of the expedition established three colonies that became the basis for the major power blocs in terran space: the Confederacy, the Kel-Morian Combine, and the Umojan Protectorate. The corrupt Confederacy was overthrown by terrorist and revolutionary Arcturus Mengsk during the chaos of the zerg invasion. Now the Terran Dominion has emerged from the ashes of the old Confederacy as the dominant power, ruled by none other than Emperor Arcturus I.

Forced to adapt to the harsh existence on the mostly lifeless worlds of the sector, the terrans are masters of survival. With neither the advanced technology of the protoss nor the natural prowess of the zerg to rely on, the terran military forces consist of a varied mix of units. From basic but effective infantry like the marines to heavily armed battlecruisers, terran units rely on solid armor, plentiful firepower, and strength in numbers to hold the line. Terrans excel in defensive situations where their bunkers and siege tanks really shine.

With their highly advanced technology and potent psionic abilities, the protoss once considered themselves the most powerful species in the galaxy. Their war with the zerg has proved otherwise: even the most individually capable warrior cannot overcome such insurmountable numbers. The lesson has been a hard one for the protoss, for their society is built around core philosophies that have been rigidly adhered to for over a thousand years. However, the zerg invasion of the protoss homeworld of Aiur has brought the race to a crossroads: the protoss must embrace change if they are to survive and prevail. Now new tactics and technologies are being brought to bear in the increasingly desperate battle against the zerg, and ancient, terrible weapons the protoss set aside long ago are being unleashed.

The protoss have never been a prolific people and have traditionally bolstered their numbers with a variety of robotic war machines. Individual protoss warriors are unsurpassed in their skills, greatly enhanced by the combination of technology and formidable psionic strength. Nonetheless, the protoss must rely on mobility and surprise to maximize their advantages without getting drawn into a battle of attrition. One of their greatest strengths lies in their fleet, which boasts a variety of ships powerful enough to pound an enemy to atoms.

The zerg are a race entirely unlike the terrans or the protoss. They are composed of many different species integrated into the Swarm via zerg infestation. These creatures are rapidly and selectively evolved into deadly and efficient killers to further the driving zerg imperative of achieving absolute domination. The zerg make no use of technology to create their weapons, armor, or starships. Instead, these functions are efficiently fulfilled through biological adaptation and planned mutation of the zerg strains. Even zerg buildings are in fact specialized organs within the living, growing organism of a zerg nest.

When the zerg first arrived in the Koprulu sector, they were unified by their absolute obedience to the zerg collective sentience known as the Overmind. The Overmind ultimately directed the actions of every zerg creature in the Swarm, functioning through a hierarchy of lesser sentiences. The first and most important tier of these consisted of the cerebrates, each entrusted with direct control of a sizable section of the Swarm. The cerebrates' commands were disseminated in turn by the overlords, which directly ordered and controlled the mass of zerg creatures both in their nests and on the battlefield.

Although the Overmind was primarily driven by its desire to consume and assimilate the advanced protoss race, it found useful but undeveloped material in humanity. Taking a powerful terran psionic, Sarah Kerrigan, the Overmind evolved a new and unique creature: the Queen of Blades. When the protoss destroyed the Overmind during the invasion of Aiur, the Queen of Blades manipulated the dark templar into eliminating the surviving cerebrates. As a result, she came to dominate the Swarm.

AH/G-24 Banshee: A cloak-capable gunship.

Battlecruiser: Each battlecruiser can be upgraded to have either the Yamato Cannon ability or the new Missile Barrage ability.

Ghost: Equipped with a new sniping ability.

Hellion: Formerly known as the Jackal, this fast vehicle is armed with a flamethrower suited for destroying masses of weaker units.

Marauder: The replacement for the firebat.

Marine: Will be able to upgrade hit points with a shield.

Medivac dropship: A dual-purpose unit combining the old dropship and the medic, it is capable of transporting ground units and healing infantry.

Reaper: Uses dual pistols, can jet pack up and down ledges and lay mines.

Nighthawk: Formerly known as the Vulkan and Nomad, this air unit creates smaller independent munitions.

SCV: Repair will be "autocast".

Siege tank, Crucio: Can transform into a stationary 'siege cannon' mode, allowing it to strike targets at a greater range.

Thor: This intimidating mechanical unit is named after the Norse god of thunder.

Viking: This Terran vehicle can transform from a walking robot into a spacecraft.

Carrier: A powerful air unit. Carriers do not have their own attacks but creates interceptors to fight for them.

Colossus: The large quad-legged vehicle fires multiple lasers per attack in a splash pattern well-suited to destroying swarms of weaker units. This unit can also traverse differences in terrain height due to its long legs, and will appear to step over ledges and other obstacles due to the inverse kinematics system.

Dark templar: A permanently cloaked stealth warrior.

High templar: A physically fragile unit with strong psychic abilities.

Archon: Created by merging two templar units, the archon is a powerful melee unit with a very durable force shield and a strong energy-based attack.

Immortal: Dragoon-like walker with a strong defense against powerful attacks, but vulnerable to weaker attacks.

Mothership: A powerful flying unit that consumes an extreme amount of resources to produce. It has powerful special abilities.

Observer: A cloaking air unit that functions as a detector.

Nullifier: A ground support unit.

Phoenix: An aerial fighter.

Probe: The builders of the protoss race. Gathers gas and minerals.

Stalker: A dragoon-like Dark Templar unit, able to blink (short-range teleport) and deliver ranged attacks against air and ground units.

Void ray: Formerly known as the warp ray, this flying unit deals damage with a blue energy beam that does more damage as it focuses on the same target. Good versus heavily armored targets like buildings, weak against small arms fire.

Warp prism: Formerly known as the phase prism, the warp prism is a dual-purpose unit, able to transport units or to create a warp matrix field like the pylon.

Zealot: Will have a new charge ability, allowing a zealot to quickly close the distance between itself and an enemy unit.

Corruptor: Attacks air units and "corrupts" them rather than destroying them.

Drone

Hydralisk

Lurker

Infestor: Can move while burrowed.

Larva

Morphalisk
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Mutalisk: The main air unit of the zerg with high movement speed.

Swarm guardian: Similar to the original guardian, evolved from the mutalisk, but spawns broodlings when it strikes.

Overlord

Overseer: An evolution of the overlord. Works as a detector, and is considerably faster than the overlord.

Changeling: A spy created by the overseer.
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Nydus worm: The new transport structure for the Zerg, similar to the nydus canal. Produced by the overseer.

Queen: The new Queen is very different, being a powerful attacking ground dwelling support unit ideal for Zerg defense. Multiple queens can be built.

Roach: Has a fast regeneration rate.

Ultralisk: Now has four scythes instead of two. In addition, it can now burrow.

Zergling

Baneling: This green rolling unit is mutated from the zergling. It has a suicidal attack.