Billie Piper
The series began in April 2008, and after several cameo appearances, Piper made her official return as Rose in the series four final episodes Turn Left, The Stolen Earth and Journey's End. She has not said whether she will be reprising the role again, although on Doctor Who Confidential she said that she thinks "It's never really the end for the Doctor and Rose" but it probably was "for the foreseeable future".