Certainly high on the list is Bambi. I have never seen it. But I can tell you that Bambi's mother dies. I think she is shot or something, I don't know. How do I know this? Dumb question - everyone knows this. It isn't even a spoiler any more, it simply is.
Oh, and Soylent Green is [spoiler:haodj5e0]also a commonly spoiled movie[/spoiler:haodj5e0]
Any others?