Multiple sources, including our buddies at Joystiq, are reporting that Blizzard is bringing a big surprise to their World Wide Invitational event, held in South Korea on May 19. And the rumors say that the surprise is none other than Starcraft 2. As in a new race, lots of changes to existing units, and a glorious return to Blizzard's RTS brilliance.
It may not be, of course. Blizzard hasn't confirmed anything yet (of course they haven't), except to say that they will be making a big announcement then. They have talked about Starcraft 2 before, and if they're going to release a new Starcraft anywhere, it might as well be in South Korea. But of course the next WoW expansion has to be announced sometime, and Diablo 3 has been going through the rumor mills for a long time, too.
No matter what Blizzard announces, you can bet it'll be seen in some form (hopefully playable... drool) at Blizzcon in August. And then whatever it is, considering Blizzard is making it, we'll probably see it on store shelves in early 2015.