JK Rowling has announced the title of the 6th Harry Potter book. Her website is rather spiffy, and she revealed the title behind a door with a wall behind it. (If you want to check it out for yourself, click on the scrunchy hairband sort of thing at the front of her site.) For the solution on how to get behind the wall look here: Wizard News: J.K. Rowling announces title of Book 6
In her news section, Rowling said that Half Blood Prince was nearly the title of Chamber of Secrets. She would not reveal who the HBP was, other than to say it is not Harry or Voldemort. I put my money on Colin Creevey.