Okay: Saturday is almost here, so this is my gloriously optimistic list of stupid predictions.
The four remaining Horcruxes are based on the suits of the Tarot: we know of Hufflepuff’s cup, and Slytherin’s amulet/pentacle, but the other will be Ravenclaw’s wand and Gryffindor’s sword. Yes, I know Dumbledore thinks it isn’t.
The broken statue at the Ministry of Magic showed four races: wizards, centaurs, goblins, and house-elves. Harry will need the assistance of each race, for each Horcrux.
One Horcrux, possibly Slytherin’s, will have been stowed in Gringotts Bank, possibly by Kreacher. Harry will retrieve it with the help of Gringott’s curse-breaker Bill Weasley. The very first book contained a rumor that there were dragons below Gringotts, and I think it’s true; so Harry may need Charlie Weasley as well. Goblins may help Harry here, since they run Gringotts. Harry can get into the Black family vaults because he’s the heir.
One Horcrux will be in the Dark Wood, where the centaurs will help, and possibly the spiders, the Ford Anglia, and the flying motorcycle. This will probably be where the giants will come into play as well.
One Horcrux will be in Hogwarts itself. Fred and George, and the Marauder’s Map, will be useful here. Somehow one of Fred’s and George’s fake rubber-chicken wands will be used at a critical moment. The house-elves all appear to be here in Hogwarts, so that’s where they will be of use.
One Horcrux will be in some location we haven’t seen before.
Since “love will save you” is a theme of the series, the couples are off the table. I’m thinking the ones who die will be Draco, Neville, and possibly Snape.
Dudley Dursley will do magic, which is about the only thing that will get the Dursleys to accept magic, because it’s unthinkable they’d reject their only son.
Voldemort won’t die, but instead become a powerless spirit or ghost or something.
Killing Fenris will cure Lupin and Bill.
Snape will sacrifice himself to save Harry.