"Doppelgaenger" movies
 

Hi ,
I just wanted to start a dicussion regarding movies dealing with "Doppelgaenger". The genre would be horror of course or thriller/psycho. Which movies do you know and which ones are your favourites dealing with that matter in the broadest sense.
Personaly I like those with a conspiracy and/or a good twisted plot. Something like "Fight Club" or "Following".
Im eager to read you recommondations.
(Excuse me for my probably bad english.)