Regarding that last one, Heinlein used to call me every year to sign me up for the blood drive at the WorldCon. He called once when I wasn't home and my youngest son took the call. Heinlein chatted with him, and described to him the plot of the story he was then writing, which turned out to be Door.
Another good one is David Gerrold's The Man Who Folded Himself.
I'm currently writing a novel about time travel, and one of the key issues is, would you try to change the past? In the novel, that's called "time crime," and the penalties for trying it are very severe. My main character is sorely tempted once to try it, but decides against changing the past.