A spot of speculation:
I was just reading some of the tidbits about book seven that Ms. Rowling has let out, and just wanted to toss some ideas out there.
1. Dumbledore's Ancestry and Family will be explored. There's a little to suggest he's somehow related to the Weasleys, but I think that that's most likely complete bull****. Many believe him to be the descendent of Gryffindor or Merlin... But I still believe Harry to be the descendent of Gryffindor...
2. Sirius' two-way mirror communicator and flying motorcycle will play a role in the next book. Since Harry has not passed apparition, I bet you the motorcycle will be a primary means of transport as he seeks out the other horcruxes across the english isles and very possibly beyond. The Mirrors I think will be Harry's way to communicate with the order, or possibly even Ron and Hermione. One thing that I definitely noticed was that Harry was very much emotionally unresponsive at the end of the last book, so I think he's going to need to learn what love is for himself so that he can defeat Voldemort. That theme is too important not to play a major role in the final book... I sort of see him getting more and more distant, dressing more like sirius as he flies his motorcycle getting clues on his own as Hermione and Ron do research about this and that from 12 Grimmauld Place. I bet that it'll be Ginny who brings him back to himself and shows him the strength of love somehow giving him the power to destroy Voldemort.
3. We still haven't heard anything about Dumbledore's will, and I gaurentee there will be some things he leaves to Harry... For one, I think Harry will get his penseive and various memories instructing Harry about destroying horcruxes... I also think having the penseive will get him to look at more of Lupin's memories about Snape, revealing the fact that he was in love with Lily... I've mentioned that theory before, Snape defected to Dumbledore's side the second he endangered Lily's life... He hates Harry because Harry has the spitting image of his father, but his mother's eyes, which is important because there have been a few times where Snape has stared into Harry's eyes, thinking. Honestly, I think Snape's going to find a way to get in touch with Harry, perhaps sending him important memories...
4. The final showdown HAS to happen at Hogwarts. Half-Blood Prince cemented the importance of the school to Voldemort and even highlighted the fact that harry and voldemort had that in common. I also have this great image of the entire school readying itself for battle... Death Eaters, Giants, Werewolves, Imperi, and Dementors marching on the Castle, The Order of the Pheonix at the forefront of the battle, but also the House Elves, the Students, Hagrid, Grawp... Perhaps the Centaurs and even the Giant Squid could take a few out. I can picture it all coming down to this... I see Draco and Lucius versus Ron and Arthur Weasley... I see Lupin and Bill (and perhaps even a more Veelaesque Fleur) versus Fenrir Greyback... I really hope I'm right about this...
5. Harry is the final Horcrux... His scar at least... But honestly it makes the most sense. If not, its some artifact left in Godric's Hollow, probably created with the death of James Potter, perhaps a relic of Gryffindor. Nagini is CLEARLY a Red herring, as Voldemort would have never used the death of someone so trivial as the guy who worked on the old Riddle Mansion. Also: People need to stop saying there are Seven Horcruxes, when there are only six, with the seventh piece of his soul resting within his body. The others are/were the locket (possibly the unopenable locket found in the Black house, particularly if RAB is Regulus, which seems to be the consensus.), The cup of Hufflepuff, the destroyed diary, the disenchanted ring, and then two mystery objects. Nagini, as I said, i think is a red herring, but I bet he found something Ravenclawy, perhaps with some connection to Luna Lovegood. But I do think Harry is the real deal... Harry's connection to Voldemort throughout the series, particularly in book five, seems almost as if a part of Voldemort's soul was a part of Harry...
6. Deathly Hallows means Dead Saints, AKA Dead people who will help Harry somehow from beyond the grave... Sirius and Regulas Black, Dumbledore, and perhaps even Harry's Parents... All through memories and whatnot... I think that will be a major theme in the book, but I dont think any of them will be coming back in any real sense... What they left for him after they died will be what helps harry... Anybody think that once Harry comes of age he might inherit some more Family heirlooms?
7. Hermione or Ginny will die... I feel sure it's going to be one of those two