Harry Potter (blush)
Bloggers often write about books which they have read, but rarely admit to reading Harry Potter books (come one don't be ashamed everyone does it)
I'm goint to try to guess some of the content of the final book. Spoiler warnings when appropriate.
I don't see many hints from books 1-4 except that Peter Pettigrew has to do something useful (like Gollum).
In book 4 (Chalice of fire) Dumbledore shows an expression of fierce triumph when he learns that Voldemort has reconstituted his body using Harry's blood. He doesn't explain, but this must be important.
In book 5 (order of the Phoenix) we learn that only one of Harry and Voldemort can live. Not sure that means what it seems to mean.
Snape had 3 very bad memories and we have only shared one.
When cleaning 12 Grimauld Place a heavy locket which no one could open was found.
Kreacher tries to hide Black family heirlooms.
In book 6 (half blood prince) we encounter the concept of Horcruxes which are various objects which hold part of Voldemort's soul. One bit is in his reconstructed body, another was in the Riddle diary (killed in book 2), another was in a ring destroyed by Dumbledore.
One is clearly in a locket once belonging to Slytherin.
This was replaced in its former hiding place by an ex follower of Voldemort who signed R.A.B. . One Regulus Black (brother of Sirius) was once a follower of Voldemort. He was quickly killed after he tried to switch sides. I assume he is RAB and that the locket is the one found in 12 Grimauld place. I guess that there will be an effort to find where Kreacher hid it, then it will be discovered that Fletcher sold it. This should be good for hundreds of pages.
Another is likely to be Helga Hufflepuff's teacup. No idea where it is. Hundreds more pages to find if it is the horcrux and, if so, where it is,
The sixth bit is likely to be in the Snake Nagini (so guessed by Dumbledore)
The seventh is, I am quite sure, in Harry Potter. Clearly he is linked to Voldemort and Nagini. I don't know how we are supposed to pretend we haven't noticed.
As to the denoument, I risk ruining much better books, which also feature a school of magic, written by Ursula LeGuin (A Wizard of Earthsea, The tombs of Atuan and The farthest shore, Tehanu all well worth reading). I think the key is to be found either in denoument of A Wizard of Earthsea or that of The Farthest Shore. Won't say what they are, but each has a moral and both seem to potentially fit the Potter series. I'd say that Dumbledore's unexplained expression in book 4 suggests that it will be a Wizard of Earthsea moral. Others claim to know it will be the other.
The ring bears the "Peveral" crest. This family is not otherwise mentioned. This must be a hint somehow.
The injury Dumbledore received when destroying the ring was never described. I think that in books 6 and 7 as in book 1 Snape is set up to appear to be guilty but is innocent.
Roughly, I guess something about destroying the ring made it necessary to kill Dumbledore (as in the bit of Voldemort was in him or something). Snape promised Mrs Malfoy that he would. Later he is arguing with Dumbledore that he doesn't want to do something and Dumbledore says he promised so he must. For some reason Dumbledore freazes Harry when he could have saved himself. He seems very calm till he sees Snape who kills him. It all makes sense if Dumbledore wanted Snape to kill him and feared Snape wouldn't do it. The aim may have been to give Snape absolute credibility with Voldemort.
Neville Longbottom has moved from being a geek to being an extraordinarily brave hero type. The prophesy could refer to him not Harry. He might have to do something very unpleasant to end the series.