Short stories, novellas, and other forms of short fiction are getting a makeover with the prolific access to publishing channels and innovative marketing campaigns. Short stories, the backbone of short fiction, prevails with short story contests and award-winning anthologies. Traditionally defined as stories in length from 1000-4000 words (some go longer, though, up to 20,000), short stories have been the entrée for many an author to get noticed. Many short stories have been adapted into plays, films, and other media. Check out the Goodread's list of all time bests.
The novella, once out of fashion in the publishing world (even though many classic novels, like Animal Farm, Of Mice and Men, and The Metamorphosis, could be considered novellas based on lengths from 20,000 - 50,000) are breathing new life marketed under new names. James Patterson and Harper Collins' recent foray into the short novel - they call them "Book Shots" - focus on short, genre fiction, no more than 150 pages (about 30-40,000 words or so). Released this month, the author's first two releases came out strong with sales of 30,000 copies in the first week or so! These new short novels can be read quickly and feel like watching a film. Expect other publishers to pursue this rebirth of short fiction. They'll be looking for content, content, content...a great opportunity for writers to get in the game.
If you want to go even shorter and really flex your word-efficiency, you can write flash fiction - defined as a few hundred words (or shorter). These are fun tidbits from any genre that tell a story or evoke a mood...and can be read in minutes. Read some of the genre's top flash fiction at Flash Fiction Online. You can learn about the format and submit to their literary magazine.
At the micro end of the short fiction scale, #twitterfiction, allows writers to create the most creative narrative, tweeting as adopted personas, or tweeting a story from multiple characters' points of view. Check it out if you have a few seconds.
Whatever form your short fiction takes, there's a home for it these days. So get in the game...and keep it short!