Now that you mention Hitchcock, I wonder if _Vertigo_ would count. There are the two women, Madeline and Judy. Well, I know they're not actually two different women but he *thinks* that they are. Hmmm. This is of course a sort of forced fantasy because he deep down knows the truth - could you called that the "doppelganger by desire"?
< aaach!!!! . . . how could we have forgotten?
< perhaps the most striking pair of doppelganger
< in cinema are hitchcock's two charlies