The ending of a movie is often the part that sticks with you long after you've left the theatre. Done right, a good ending feels like the logical point at which the story you've just witnessed should wrap itself up and come to a conclusion. Better yet, a great ending will give you something to mull over or think about during the car ride home.
Whereas most movie endings are fairly simple in their execution (the hero kisses the girl whilst orchestral music swells), there are some endings (more complex in nature) that have succumbed to a fair amount of misinterpretation over the years. This kind of thing seems to occur mostly in films with purposely ambiguous endings, or those that choose to leave audiences without an "easy" answer.
All movies are open to interpretation, of course, and there's certainly no "definitive" answers to be associated with any kind of art. But take a look at the movies assembled here, all of which have famous endings that movie-goers seem to misinterpret on a regular basis.
Sometimes it's the filmmakers' fault for not making things clear enough, though now and again it comes down to good old-fashioned ignorance...