Blizzard has announced that the invites to the closed beta for StarCraft II: Legacy of the Void will be going out March 31st. Gotta hand it to the folks over at Blizzard, they sure do know how to stretch the life out of an IP with Starcraft II getting close to 5 years old now. Of course when it's one of the best and most played RTS games in the world, that's not the toughest call to make. More details about the beta and the sign-up page can be found at the StarCraft website. This expansion marks the conclusion of the StarCraft II story, and I can imagine anyone who's fallen in love with the game over these last 5 years will want that closure.
Legacy of the Void will feature new maps (Ruins of Seras, Lerilak Crest, and Orbital Shipyard) and a new Protoss unit, the Adept, which has a ground-only ranged attack and can send out a non-combat duplicate which it will later teleport to after a fixed duration.
If you're new to StarCraft II, check out our review from waaaaay back in 2010.