It seems like every HP fan page has them: rumors, theories, etc. Here are some confirmed facts and various theories that may be possible for the next two books.
*Neither Harry nor Voldemort is the half-blood prince.
*Now that Voldemort's back, the muggle world will begin noticing more 'odd things'.
*Since Neville's wand was broken in the Dept. of Mysteries, he'll be getting another one.
*More information about Voldemort's birth and Harry's relatives will be revealed.
*Ron and Hermione will turn 17 and thus be of age to Apparate during the school year.
*A new Minister of Magic, but it isn't Arthur Weasley or Harry Potter.
*Crookshanks isn't an animagus
*Lily Evans Potter isn't alive, nor was she a Death Eater.
*Neville isn't the son of Peter Pettigrew.
*Remus Lupin doesn't have a twin.
*Dumbledore and Harry are not related.
*Harry gets a little romance, but not with Cho. (Ginny?)
*We get to find out why Dumbledore trusts Snape.
*More info on the Snape/Sirius rivalry
*Snape's worst fear will be revealed eventually, and it's supposed to be 'important'.
*Hermione and Draco will not end up together.
*More on Harry's scar
*Appearances from Narcissa Malfoy and Tonks
*Important info about Lily Evans Potter (the rumored relations with Snape, or pureblood perhaps?)
*The professions of Harry's parents is important, as is the fact that he has his mother's eyes and that his mother's wand was good for charms.
Voldemort doesn't have any kids.
These are just some confirmed facts; there are others.
The next death
There are rumors of another death floating about, so I thought I'd offer my two cents on who it might be.
1. Ron Weasley: Remember when Ronan told Hagrid that the innocent were always the first victims? First the unicorn died, and then Cedric Diggory. Cedric's wand contained unicorn hair, as does Ron's new wand. Foreshadowing, perhaps?
2. Remus Lupin: Two of the Marauders have already died-James Potter (Prongs) and Sirius Black (Padfoot). Is Remus next?
3. Peter Pettigrew: Same reason as the above. Traitor or not, he was still a Marauder. I think that before Peter goes, however, he will somehow return the favor to Harry, who spared his life in book 3.
4. Neville's grandmother: Most of Neville's family is either dead or in the mental ward of St. Mungo's. His parents were members of the Order, and his family is apparently a threat to Voldemort.
5. Neville Longbottom: See Neville's grandmother. I doubt Neville will be next, but it's possible.
6. Susan Bones: Most of her family was killed by Voldemort. It appears as if only her aunt Amelia at the Ministry has been spared. Susan could very well be next on the list.
7. Amelia Bones: See Susan Bones. She might come before Susan, considering how she's in a position of power in the Ministry.
8. Albus Dumbledore: Well, he is getting on in years. JK may be going for the 'you have to face your enemy without the mentor's guidance' bit.
9. Molly Weasley: I would really hate this, but at least two of her close relatives (Gideon and Fabian Prewett) have been killed by Voldemort's followers. More foreshadowing?
10. Hagrid: Not likely, but possible. Hagrid is the only one who can prove Tom Riddle opened the Chamber of Secrets. Not that it matters now, but it still might be important.
The half-blood prince 1. Seamus Finnegan: He's half and half, and the sorting hat took a full minute to sort him. What was the hat talking about with Seamus?
2. Dean Thomas: Also half, but he thinks he's muggle-born. His father was a wizard who left his family in order to protect them. Was this the standard case of a wizard protecting his family from Voldemort, or is there another reason?
3. Neville Longbottom: Although he's a pureblood wizard, it's still possible for him to have some muggle blood. Why were his relatives hunted down by Voldemort?
4. Hagrid: Well, he is a half-giant. Hagrid's mother was giant royalty (I think), and Hagrid's wand is made of oak, which is sacred to many chief male gods (Zeus/Jupiter, Thor, etc) and stands for strength, power, and dominion amongst other things.
5. Ginny Weasley: She's a pureblood, but no one ever said what the 'half' in half-blood prince was. In book 5, Fred & George talk about Ginny's bat-bogey hex and say 'Size is no guarantee of power'. What if Voldemort's possession of Ginny left behind some lasting impression-perhaps power-wise, and possibly in the way of a blood link?
6. Godric Gryffindor: The Potters lived in 'Godric's Hollow', which was confirmed by JK to be a muggle village. Now, why would a muggle village be named after Godric Gryffindor? Could he have been a half-blood?
