A new South Korean source claims that, according to a leak, Blizzard will be announcing StarCraft 2 at the World Wide Invitational, on the 19th of May 2007.
Update May 19th: Confirmed!
And here we go:
After years of waiting, Blizzard Entertainment seconds ago announced that StarCraft 2 would be the new game! "Looks strikingly similar to SC1" according to IGN.
See also: http://www.starcraft2.com