All of Neil Gaiman's short story collections. My copy of
Fragile Things is ancient, and the shiny red leaf pattern is wearing off the cover, but I still reread the stories in there. I love the simplicity and clarity of the writing, and the magic or spec elements in the everyday world.
To be honest, even better than reading his shorts, is
listening to Gaiman read them. If you ever get the chance to go to one of his readings, don't miss it. He does them all around the world these days. But we also listen to his audio books that are suitable for kids if we are travelling with the car.
Other short story writers: All the classic SF writers that I read when I was a young teenager. (That's Bradbury, Asimov etc.) And I've read so many others since then, its hard to isolate one. But every now and then, if I want to find a novel I'll enjoy, I'll read a collection of shorts and choose a novel by my favourite.
The new
Anywhere But Earth anthology of Australian spec fic writers has some excellent SF short stories in it, including ones by Richard Harland and Margo Lanagan. It is a huge book!