One of my favorite short stories, coming from my time in public school, is Ray Bradbury's "There Will Come Soft Rains". The title (and premise) comes from a work by a poet I love, Sara Teasdale, and it's beautifully written. It's admittedly not the most complex story in the world, but it hit me hard in my formative years, and I fell in love with it.
What's your favorite short story? Why?