We know that Blizzard has at least two StarCraft II expansions, Diablo III, MMO Titan and World of Warcraft expansions planned, but it seems that the developer has something else up their sleeve that they have yet to announce. According to a job posting on the Blizzard website, the developer is looking to hire a Software Engineer to work on development tools and content management systems on an unannounced title. The description calls the job, "a key role on a new and exciting project within the company."
What this new project is has yet to be revealed, but given that we know what Blizzard has planned for their current lineup, this could hint at a possible new IP. Stay tuned and we'll update you when we have more.