It’s hard to name some top ten lists (music, films, etc.), but my top short story is a clear choice. The best short story I’ve ever read is Flowers for Algernon. If you’re ever able to read it, don’t read the extended novel (really novella) version–it’s not as good. The short story version is twenty-six or so pages long, and won the Hugo Award for best short story in 1959. When the Hugo was presented by Isaac Asimov, Isaac cried out “How did he do this? How did he write such a story?” and raised his face to meet the eyes of the giant who created such words. Then he lowered his gaze to see normal-sized Daniel Keyes, who said “When you find out, can you let me know? I want to do it again.”
The movie Charly with Cliff Robertson was made (as I recall) essentially from the short story and isn’t bad at all (Robertson is excellent, but the cinematography makes it very clear at times that this is a ’60s movie). The play was made from the novel version–it’s sometimes popular in high school productions (my own high school performed it during my junior year).