Contemporary writers seem to take pride in their ability to author voluminous novels. Even when they write short stories, they're often too long, and they're seldom as interesting as they ought to be. The New Yorker may be a good measure for what's hip and likely to make a lot of money, but if they're willing to publish a short work it's also likely that the story is pretentious and probably in poor taste.
Some of the best short stories are detective fictions. Genre-specific works don't usually qualify as high art, but the ability of men like G.K. Chesterton, Edgar Allan Poe, and Sir Arthur Conan Doyle to distill a comprehensive plot with fully-realized characters into a few pages borders on genius. That Chesterton and Doyle could do it dozens of times with the same characters and keep readers interested is testament to their powerful imaginations and consummate creativity.
There are plenty of fine literary short stories, of course, though most were written between 1860 and 1960. It took awhile for the short story to grow up as a form, and it's zenith was relatively short-lived. Mark Twain is arguably the best American short story writer, capable of evoking extreme pathos and wild humor simultaneously. His best stories are basically literate presentations of oral-tradition Americana, crafted with extreme care but seemingly careless in their dialect-ridden roughness.
Many writers' excellent short stories are often overshadowed by a single brilliant longer work. J.D. Salinger, for example, wrote some of the best short stories of the 20th century (especially among those written to an artistically-inclined upper-middle class), yet no one remembers Seymour: An Introduction or To Esme, With Love and Squalor because the only Salinger work they've ever read or heard of is Catcher in the Rye.
In some ways, short stories are a better gauge of an author's ability than his novels. Short stories require a precision of style, a tightness of plot, and a coherence of vision that novelists can get away with applying more loosely. It's important, therefore, to keep them short; otherwise, you're kind of missing the point.
Novellas are the murky territory between short stories and novels. They aren't short stories, however, just novels that are easier to read or fit in your back pocket. We've limited our selection in this category to actual short stories. If you're a writer (or want to be), short stories are some of the best material you can read to improve your own craft. If you're simply an avid reader, they make some of the most enjoyable fiction available.