or in the case of Britney Spears because she felt like it:
Sigourney Weaver in Alien 3:
Cameron Diaz in an upcoming film:
Natalie Portman in V for Vendetta:
Of course no one can forget Demi Moore for G.I. Jane:
John Travolta in an upcoming movie - he looks good with his head shaved, much better than with a hairpiece:
Cate Blanchett for the movie Heaven:
Persia Khambatta for Star Trek: Original Motion Picture
Robin Tunney for Empire Records