Here's some confirmed information (meaning from interviews Rowling has done) about book 7:
Viktor Krum will reappear (I wonder what his role will be. I hope Ron's reaction isn’t to predictable)
Dolores Umbridge will be back (god it would be annoying if she has a significant part)
Something important will be revealed about Petunia; however it won’t be that she is a squib (that has me really thinking, especially after her actions in ootp)
The two way mirror will be back (that's probably the most intriguing revelation; what purpose does it have? Could it somehow be linked to Sirius? Would the image that Harry sees have changed since book 1? Could it now include Sirius and maybe Cedric?)
We will not have any doubt on where Snape’s loyalties lie (that had to be included in the final book)
Viktor Krum will reappear (I wonder what his role will be. I hope Ron's reaction isn’t to predictable)
Dolores Umbridge will be back (god it would be annoying if she has a significant part)
Something important will be revealed about Petunia; however it won’t be that she is a squib (that has me really thinking, especially after her actions in ootp)
The two way mirror will be back (that's probably the most intriguing revelation; what purpose does it have? Could it somehow be linked to Sirius? Would the image that Harry sees have changed since book 1? Could it now include Sirius and maybe Cedric?)
We will not have any doubt on where Snape’s loyalties lie (that had to be included in the final book)