Science Fiction Weekly reports that J.K. Rowling is pondering the idea of another book with Harry Potter in it, even though he might not be the central character! SFW quotes the London Daily Mail in discussing the "hints" that Rowling has dropped. Don't get your hopes up—she also said that although her oldest daughter is lobbying for another book in the series, she herself would like to wait 10 years. And, she's already working on an adult novel and a "political fairy tale," as well as some "charity work" (the charity work doesn't sound like a writing project).
I'm tagging this as "Harry Potter" because let's face it, those books are practically their own genre.