Ten most visually stunning (in order):

1/  CITIZEN KANE (One of the great "special effects" films of all time...hundreds of process shots in aid of a "realistic" story...stunning!)
2/  RULES OF THE GAME (Renoir's fluid, moving camerawork and the choreographed movement of the actors is unsurpassed.  It's like a ballet without the ballet)
3/  BLACK NARCISSUS (A film set in the Himalayas that was shot entirely in the studio.  Also the most stunning use of flashbacks ever attempted)
4/  THE CONFORMIST (Not a film I particularly like, but the perfect melding of both style and substance).
5/  THE COOK, THE THIEF, HIS WIFE AND HER LOVER (Greenaway and cinematographer Sacha Vierny seduce and repel often within the same scene...Audacious)
6/  MCCABE AND MRS.  MILLER (Zsigmond's "flashed" neagtive and Altman's propensity to zoom the camera to reveal a characters inner truth, makes this the most beautiful American film of the '70's)
7/  BELLE DU JOUR (Buñuel's first film is also his most visually stunning thanks to Sacha Vierny's camera and Catherine Deneuve's face)
8/  GERTRUD (Dreyer does what no other director is capable of doing.  He turns that camera on and lets the actors "act".  No camera moves.  No cuts.  Just pure, unadulterated emotion).
9/  MY DINNER WITH ANDRE (One of the most action packed films I have ever seen.  Louis Malle keep his camera close to the faces of Andre Gregory and Wallace Shawn and lets them talk.  The result is that WE are forced visualise the stories that Gregory tells us.  A case of "Virtual Reality" made prior to the coining of the term)  
10/  THE MAGNIFICENT AMBERSONS (A film in which the camera is so important that the Criterion Collection actually included a card in the laserdisc version that told you how to adjust your television so that you can see the film properly)