North by Northwest (Hitchcock, 1958)

A great example of a Red Herring is the crop scene from Hitchcocks north by Northwest.
".......Dusting crops where there ain't no crops"
Here the main character, Thornhill is sent out to meet the man who said he will explain why he has been mistaken for a government agent. We believe that he will help him however we end up seeing Thornhill being attacked by crops, and an explosion leads to Thornhill escaping without any explanations.