Here are my candidates:
IMHO, none of the remaining Hogwarts staff really rate a spectacular death. Rowling could always knock off one of the minor student characters like Cho Chang or Luna Lovegood, but that would be too easy and not carry much weight. Cedric Diggory's death was shocking but perfunctory. Their fates usually involve magic comas and such, so I think any death would have to fall closer to Harry.
My first thought was either Snape or Malfoy through some redeeming and heroic act. Think Darth Vader throwing the Emperor down that shaft at the end of Return of the Jedi. Snape's true allegience will definitely be in play, but the greater moral struggle belongs to Malfoy; Harry's secondary nemisis.
He'll have to defy his father and his house, but I predict Harry will bring him around to the good side through an act of forgiveness or mercy. Reborn, He'll be primed to make the ulitmate sacrifice.
I keep flip flopping between those two, but it won't be both.
I think Hermione and Ron are off the hook because their romance arc is far from finished.
My third possiblity is Neville Longbottom. He has slowly been rebuilding his dignity over the course of the series, and his parents were killed just like Harry's. I'd say he's ripe for a tragi-heroic guesture. Go Neville.
Ginny is certainly game given Harry's feelings for her. I can definitely see Voldemort capturing her and forcing Harry to choose her life for high stakes. Harry gets his magic strength from his capacity to love, so her peril is assured. Whether she or Harry goes depends on J. K. Rowling's capacity for a happy ending. I'm 50/50
