Naturally, I'm a big fan of the Big Three: Asimov, Clarke and Heinlein, but books that seem to me somewhat obscure but may actually be popular are Lest We Forget Thee Earth, The Adolescence of P-1, and a story about a "forever car" and another about a man who found himself in the guture when everybody was so thoroughly sane he seemed insane by comparison due to normal anxieties that he harbored, even though he was perfectly sane in his own time.