The first thing that comes to mind is Dr. Strangelove.
Yeah, that's a winner alright, one of my favourites too, and I think Slim Pickens' bomb ride is the best scene he ever played. For poignancy, pathos, tragedy, and, in the light of recent history, irony, I think Dr. Zhivago takes the prize. On the lighter side, one of the Pink Panther movies, I don't recall which one (and I concede my memory may be fooling me about this, it's been a long time), ties up all the loose ends in the plot by putting all the characters with unresolved issues into the same car, driving it off screen, and blowing it up. Bit of black humour, but it sure made me laugh the first time I saw it. And for chills and horror (no doubt a reflection of my age and experience at the time), nothing does it to me like the ending of American Graffiti. After 90 minutes of light entertainment that closely mirrored much of my own adolescent experience, which I thought was deadly serious at the time but later perceived (like when I saw the movie) as pretty trivial, reality suddenly intrudes in the form of death and war.