I don't know what else blizzard is working on at the moment but WoW is taking up a lot of their time, I'm sure. To the best of my knowledge no plans for Starcraft 2 have yet been announced, but knowing Blizzard they won't just let the franchise dry up. They'll take their time, and likely release a well crafted sequel that's true to the genre, it's what they're in the business of doing, and I've gotta' hand it to 'em, though they may take their sweet time, they do make games right.