Aunt Petunia is a Horcrux!
Well, no, not really (or if she is I'll be shocked), but I wanted to get in on the spoiler game without really spoiling anything. ;-) But I did want to write down my predictions before I hear any actual spoilers or read the book.
What I think will happen:
1. Petunia is a witch choosing to live as a Muggle.
2. One of the Weasleys will die.
3. I believe the character JK Rowling originally intended to kill off but spared is Ron.
4. Snape will die saving Harry, proving that he's "Dumbledore's man through and through."
5. Voldemort's mysterious enemy could be Regulus Black, but I think there's a good chance that it's a Muggle orphan who knew young Tom.
6. Luna Lovegood will play a key role. Dumbledore's "All you need is love" speech to Harry alluded to this.
7. Neville will die heroically.
8. Percy will be redeemed.
9. Draco will be redeemed.
10. Viktor Krum will turn up.
What I think should happen:
1. Harry falls in love with Luna.
2. Hermione saves the day by wising up, getting Trelawny drunk, and then listening to what she has to say (since Trelawny is always right.)
3. Dudley is an unexpected hero.
4. Harry dies killing Voldemort.
5. The House Elves stage a revolution, led by Winky.
6. Ginny falls in love with Neville.
Let the debates begin.