From pottermore.com (currently only available to beta users):
"Pottermore is an exciting new website from J.K. Rowling that can be enjoyed alongside the Harry Potter books. You can explore the stories like never before and discover exclusive new writing from the author."Perhaps more relevant and exciting if pottermore had started while Rowling was still writing the books, but this could be fun when it comes time for a re-read. Which may be soon, as the site is expected to be the first location where you can finally purchase e-books of the series.