Here are some screenies, etc.

Blizzard Entertainment, maker of the hugely successful Warcraft and Starcraft PC game series, reveals that it's finally working on a Starcraft sequel. According to early reports from Blizzard's Worldwide Entertainment Event in Seoul, the company plans to renew the space-combat battles among the game's three species--Terran, Protoss and Zerg--and offer a new storyline and modern graphics.
The new story takes place four years after the 1998 expansion pack Starcraft: Brood Wars, and features new planets, characters, units, weapons and combat. For more information read the preview posted by CNET Networks' GameSpot.
On its Web site, Blizzard makes fun of itself and the long wait for this sequel. Starcraft was originally released in 1998. No release date for Starcraft II has been set.

One of the new features of Starcraft II will be massive battles which could involve hundreds of units. Here the Terrans face swarms of Zerglings.

Starcraft II will feature new units such as the powerful Protoss Colossus, which resembles the gigantic alien walkers from the movie War of the Worlds.

Another new unit is the Protoss Immortal, a crab-like tank with dual mounted turrets and an emergency shield.

Protoss will have the ability to warp to new locations. But game developers are sure to counter this with new moves by the Terrans and Zerg.

The Zerg attack a Terran base.
Source and more concept art, etc.