The entire original trilogy of Star Wars was a huge toy commercial. Lucas did something no other filmmaker had done at the time... he traded away film profits in exchange for sole ownership of the merchandising rights. ("Merchandising, merchandising! Where the real money from the movie is made!" as Yogurt would say). At the time, merchandising meant lunchboxes and the like, so Fox went "uh, okay dude, go for it."
Also, the book The Princess Bride is tripe. Take out 90% of the comedy from the movie and insert torture, tedium, and gloom. (Not Goldman's fault, blame Morgenstern... the man had dozens of pages devoted to packing clothing for a trip.)
Finally, my entry, although I shall be slapped with the mighty trout of "Wha???": Dr Strangelove. It just drags on and drags on. It wastes the talents of every great actor associated with it (George C Scott, I'm looking at you). Slim Pickins had a more believable character in Blazing Saddles than he did in Strangelove. It was, on all fronts, the movie with the biggest value to hype gap in the history of films.