"The Last Question" is still one of my favourite short stories of all time (in multiple senses). It is not just that it is so clever, and has such an unforgettable last line. It is that it manages to do well and concisely what George Bernard Shaw did badly and with a ton of waffle in Back to Methuselah (I have never really been a Shavian). And Asimov was so good at writing stories as conversations.