So far, the only confirmed character returning is Sidney Prescott, to be played by Neve Campbell.
Presumably, Courtney Cox will return as Gale Weathers, though David Arquette won't return as Dewey Riley since he was killed off in Scream 5, I believe.
If Emily Mortimer's character returned from Scream 3, though, that would be great as Ghostface?
Also, if the rumors that Matthew Lillard is coming back as Stu Macher somehow, despite being electrocuted to death in the first movie, that would be awesome.