For me, Saki, Maupassant and also Somerset Maugham. I'm not well read in modern short stories and haven't read much that I enjoy, but that's probably because most writing is average and won't last, whereas we don't see the older short stories which have disappeared leaving only the best still available. I think that good short stories are few and far between because they are so difficult to write -- no room for waffle, every word counts, and they must leave a feeling of satisfaction somehow, which needn't be a plot finale.