Potter Predictions
I would say spoilers ahead, but if you haven't read them by now, I doubt you're going to.
1) Rufus Scrimgeour is Sirius' brother Regulus Black.
Why? Sirius is a dog, as is the metaphor of his namesake, the lead star of Canis Major the Big Dog. Regulus is the lead star of Leo the Lion, so it is likely that the character will have qualities like a lion or even be an animagus like his brother. We already have a character with lion-like qualities--Rufus Scrimgeour, the new minister of magic. Regulus reportedly died in the last war with Voldemort, but if he faked his death and went into hiding, he would not be the first to have done so. If he assumed another identity to gain a better position in the fight... again, he would not have been the first to do so.
Regulus Black would also likely be R.A.B., since he is the only known character with those initials. Given his association with Voldemort (Regulus was a Death Eater) and new animosity toward him, he would have the knowledge and motivation to go after the horcruxes/philacteries.
2) Dumbledore is dead, but will be ressurected.
You don't spend six books setting up a metaphor that you don't plan to use. Dumbledore's familiar is a Pheonix, and just as Voldemort's snake-like attributes are expressed in his snake familiar, and Harry's owl embodies Harry's own affinity for flight, the attributes of Dumbledore's familiar will articulate themselves as well.
Several points to consider:
-Dumbledore is in fact dead. There will be no cheats, like Dumbledore was only glanced by the spell and set up a dummy to fool everyone into thinking he's dead. Dumbledore is in fact dead, but will return to life, Jesus/Dionysis/Krishna-style.
-Usually in literature, when the hero must solve a quest but is guided by someone more powerful than himself, his guide must be removed so that the hero can be the one to finish the story. Harry's father figures have been systematically removed in the same vein. Dumbledore's ressurection may go against this device, although the prophesy established that Harry must be the one to kill Voldemort (or be killed). Dumbledore may still have a great task that he'll need to complete in order for Harry to go on with his. (Of course, that task may have already been completed with his sacrifice, a la Aries in FFVII.)
-Dumbledore will not be a ripoff of Gandalf. This is the same fallacy as saying humans evolved from apes when, in fact, humans and apes evolved from the same ancestor. Likewise, Dumbledore and Gandalf are expressions of the same archetype.
3) Harry will, at some point, die.
In order to fulfill the criteria of Joseph Campbell's monomyth, the hero must at some point overcome his own death, sometimes literally dieing and coming back to life. He may not have to--some people have cited the trash compactor scene in Star Wars as Luke's moment of death, so almost any dire situation could be argued as the pivotol moment. The events at the end of Goblet of Fire may qualify, especially since it triggered his ability to see the Thessrals. I would hope that he would have to go through an even tougher trial, even if it doesn't end with him continuing to be dead.
4) It is Neville, not Harry, who will kill Voldemort.
Neville still qualifies under the conditions of the prophecy, even his "mark" may be taken by the trauma he's gone through because of his parents. It would be a spiffy little twist, especially one that will vindicate and otherwise pathetic character.
5) Harry dies on page 11 and Ron and Hermione spend the rest of the book trying to ressurect him.
Wouldn't it be cool?? Honestly, we've had six books of this guy, and of all the characters in Harry Potter, who's favorite is really Harry Potter anymore?
And finally...) The book will open at the Dursley's, there will be a sequence involving a train, we'll see an uneeded scene where unimportant characters will be sorted by a hat, shit will happen, people will go on Christmas break, more shit will happen, and everything will be resolved during finals week. Christians will complain about the decline of America to godless secularism. The end.