Ok, I'm about 3 pages from the end of OOP. I'll have to reread HBP, because so much has been clarified.
Unless I'm missing something - I think Harry will find a way to speak to the voices behind the veil in the whatever of Mysteries - without dying himself. Actually, he may find a way to release the people there and bring Sirius back. What if JKR is setting it up that Sirius died so that he & Dumbledore can either return or help together in some way....
I still think Snape is good underneath it all. I think it'll be a fight between Neville and HP on who gets to torture Bellatrix, but Neville will win because like she said - you have to really mean the Cru - whatever curse for it to stick (sorry for the whatevers - my book is upstairs and I AM NOT going up there to get it

). I think Neville will turn out to be a very powerful wizard. Hermoine has the knowledge, but she doesn't seem to do well in DDA. I don't think she'll be a very good Auror - she's too sympathetic (look at how she stopped Harry from getting the Death Eater when it had a baby's head).