Bloomsbury’s official website reveals that they will be releasing a “Celebratory Edition” of Harry Potter and the Deathly Hallows due to be released in October:

The [seventh] book in this award-winning and phenomenally bestselling series, this time in a bright, colourful and starry edition to celebrate the phenomenal international sales of Harry Potter.

The weird thing is, the description of the story is for Half-Blood Prince.  Half-Blood Prince and Deathly Hallows are the only books without celebratory editions, so, this could either be the Celebratory Edition of either of them.  You can buy the other celebratory editions here on amazon.co.uk or here on amazon.com!

Thanks Mugglenet!