It's a loaded question really.  There can only be one, as far as I'm concerned... the moment the TARDIS de-materialised around Sally Sparrow and Larry, leaving them surrounded by the Weeping Angels.  I just about had heart failure the first time I saw that.  One or two similar moments (Sally and Larry looking up to see the statue "coming towards them" after watching the DVD message in its entirety comes a close second.  Feel free to add more.
	
		
			
		
		
	
				
			 
				 
 
		 
 
		
 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		
 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		