Coturnix and Orac both have their bets up for which character will die in the next Harry Potter novel. They, and most of the betting world, believe it will be Dumbledore. Coturnix explains why.
Albus Dumbledore. Yes, that's the one. He has to die in #6 so nobody expects him to help Harry in #7. Even if JKR lets him travel far away, readers will expect him to come back in the nick of time. Even if JKR makes Dumbledore old, sick and out of his mind, the readers would expect him to get sane, strong and healthy enough to help Harry. Old Albus has to go.
The Harry Potter novels are, in essence, a coming-of-age story. In all coming of age stories, the hero must reach a point where he has to stand on his own against his foe, without mentors, without help, without anyone to fall back on, especially his wise mentor/father figure. This will be the sixth of seven planned novels, which means that Harry's final battle, in which he must face and defeat the evil Lord Voldemort, will occur in the next book. To clear the decks for this final confrontation, Dumbledore has to go. As Obi-Wan Kenobi and Yoda both had to die before Luke could face Darth Vader and finally defeat him, so will it be with Dumbledore before Harry can face Voldemort for the final time and defeat him once and for all.
I agree with their logic completely, but I'd like to suggest a counter case, just for the sake of playing devil's advocate.
First, while I agree that Dumbledore needs to be eliminated from the action and killing is the best way of achieving that, there is no reason why he has to go in book six. The final battle with Voldemort in book seven will involve plenty of twists and turns. It's possible that Rowling plans to remove him closer to the climax--say, halfway through book seven.
Last month there was a flap in the British betting community when a cluster of bets on Dumbledore were made in the village of Bungay and nearby Beccles. Bungay is home to Clays, the printers of the previous five books in the series. During the printing of book five, a forklift operator at the Clays plant stole a few pages of the book and tried to sell them to British tabloids prior to publication. This has led many to suspect that a similar security leak is to blame for the recent Bungay and Beccles bets.
That brings me to my second point, J.K. Rowling is a very clever lady and we shouldn't underestimate her. I wouldn't put staging a disinformation campaign beyond her abilities. That, at least, was my first thought when read about the bets. It's not even clear that the printing is being done at the Bungay plant this time. Some rumors say the printing is being done in Germany.
So, who do I think is going to get it. I'm really not sure. Last time, I was betting on Mr. Weasley. He was a minor father figure, a friendly adult, and Harry's only advocate at the Ministry of Magic. It made perfect sense to me that Rowling would begin to establish Harry's isolation and independence on the way to his final one-on-one with Voldemort. I was right, from a purely mythical/dramatic standpoint, even though I had all of the details wrong. This time I think Dumbledore makes perfect sense, but I'm not betting on it.
As to the other characters, the only strong feeling I have is that it will not be Snapes. Harry and Snapes have been at odds since the very beginning, even though they are almost on the same side. From the mythical/dramatic standpoint, Snapes needs a redemption. This doesn't mean he and Harry need to become friends; they just need a grudging respect and cooperation to defeat Voldemort. I don't think Snapes' redemption will be anything as simple as jumping in front of a lightning bolt to save Harry; I expect that they will be required to work together to teach Harry defense against the dark arts. Naturally, that means something will have to happen to Snapes after teaching Harry and before the final battle. If Dumbledore really does die in book six, it wouldn't surprise me if Snapes became the new headmaster.
Of course, it won't surprise me if everything I think is wrong.