What Was the Greatest Ending That Wasn't Really an Ending?

So you're reading or watching a story, and BAM it just ends, right there in the middle of everything. Sometimes the greatest way to end a science fiction or fantasy story is just to leave people dangling, wondering what happened next. What's your favorite example of a story that did it well?

In fancy literary terms, this is an in medias res ending — that's just Latin for "in the middle of things," and people sometimes start stories in medias res too. Describe your favorite in medias res ending for us below, and include some pictures, links or video too!

Use the structure I've used in my example below, for maximum clarity!

Story: Moon

What made it a great non-ending ending?

We do get some closure, because our main character escapes from the Moon and is heading back to Earth. But we don't know what he will find there. I like the not-knowing of this ending because it makes us realize how much of a triumph it was for this clone to even figure out that he was being lied to by the corporation. Now he's about to find out what the truth is back on Earth, but in a sense it doesn't matter what that is. The important thing was seeing through the lies, and finding out what he really is.

UPDATE: As many of you have pointed out, it's true that at the very end of Moon we hear some news reports that he's made it home, but we know little beyond that.