Book 7

Concerning Hogwarts:
-Snape falls for someone.
-Harry falls for someone.
-I heard a rumor that he will fancy/have a crush [on] a teacher.
-Hermione lightens up even more.
-Harry will be Head Boy.
-Hermione will be Head Girl (duh!)
-More trouble in the Forbidden Forest [Note: See 'Titles and Book Publishing'].
-Hogwarts is destroyed.

Outside Hogwarts — Home, Family, Friends and Enemies:
-Something big will be revealed about Lily Potter.
-We'll find out why it's important that Harry has his mother's eyes.
-Mr. Weasley's flying car will return.
-Sirius gets his name cleared!
-Sirius gets married.
-We find out even more about Lily Potter.
-Someone/thing kills the Dursley's.
-Lupin will be killed by Wormtail. [It is possible, since Wormtail now has a silver arm and silver kills werewolves.]

Magical Community In General:
-Harry finds out more about Azkaban (and gets a look at it).
-The Dementors return (ah!)

Titles and Book Publishing:
-The title will be Harry Potter and the Forest of Shadows.
-The last word of the book will be "scar" CONFIRMED
^{Note: This may change when JK Rowling edits the book.}

Misc.:
-Harry and Malfoy team up to fight evil
-We'll find out Professor Trelawney's first prediction
-Harry IS told why Voldemort wanted to kill him.
-Dumbledore dies.
-Pettigrew returns.

JK Rowling Tells: (all below is confirmed)
-One of the characters will become a Professor. It's not Hermione, Harry, or Ron; but JK Rowling hinted it might be Neville. (Maybe Neville could teach herbology?)
-We'll find out about the Potters' occupation and why they were so rich
-We will learn why some wizard come back as ghost and some don't. JK Rowling has told us that, "Happy people don't become ghosts."