For all you maniacal Harry Potter collectors out there, that first edition of Philosopher's Stone might no longer be the most valuable Potter-related book: the Telegraph reports today that J.K. Rowling has penned a book of fairy tales to accompany the series, but that just seven copies have been made.
The Tales of Beedle the Bard, which features prominently in Deathly Hallows, features five tales from the days of wizard-yore. Rowling included the text of one of the tales in DH, but the other four are new. Each copy of the new book "is leather-bound and covered in crafted silver and jewels." Six of them have been given "to people who are 'most closely connected to the Harry Potter books'", but the seventh will reportedly be sold at Sotheby's in December, with proceeds going to charity. That's certainly going to be an auction to watch.
I find it difficult to imagine that these tales won't make it into wider circulation, whether through an eventual trade edition or by some other means. But these seven copies will almost certainly be among the most important and highest-value HP items.
Also on the HP front, see Scott Brown's post at FBB for an interesting look at colophon variations in the American edition of Deathly Hallows.
[Update: Here's the Sotheby's page for the 13 December auction, which includes some illustrations of the Rowling artwork and the starting price for the copy to be sold: a hefty $62,000]
[Further update: The Guardian has some photographs up]
[Final update: It sold! Boy did it sell. 13 December]