It's tricky because for it to be memorable you've got to evoke some kind of correlation, relation, belonging or sympathy in the viewer/reader. To make a truly memorable scene, you really need to know your target audience. And even then it can be difficult to exactly pin point what'll strike their interest.
Strong emotional occurrences such as death, overcoming unlikely odds and even sexual intercourse are probably the easiest because most people have the experience to actively relate to that, and in turn will be able to mentally experience the scene on a more personal level.