It is being reported that Dumboldore will die in book 6 :crying and Dean Thomas is the Half Blood Prince. They say a large amount of bets have been placed on these characters in the areas surrounding the town the book is being printed in. It may or may not be true but in my experience betting rumors have a tendency to be true. I was going to include links but am afraid to because they don't get hidden like spoiler info, and I don't want anyone to click on them by accident, but if you go to www.mugglenet.com
they have a story with links to the articles.