Good short stories can begin with your character stranded on an island, lost in the forest, desert or even in a big city. Try introducing a major storm to your character's environment. Let him bunker down and begin to evaluate his lot in life. You can have your character fighting the elements to stay alive by building a shelter, making clothing or finding a cave. You can add danger by introducing animals, criminals or cunning individuals who will take advantage of your character.
Good short stories can be reflections on personal insecurities or problems. You can introduce the devastation of alcoholism on your protagonist. Let the reader feel the pain the individual is feeling when she drinks, the loss of self-respect and the eventual bottoming-out. Let the reader see the battles going on inside the alcoholic's mind as she fights back and eventually conquers, or loses, the battle with alcohol.
Man against machine can be interpreted into a short story topic and it doesn't even have to have a machine in it. It can be the machine of politics. You can have your character fighting an politician that's so deep into the bowels of the industrial machine that he or she is committing crimes against common everyday people by selling out to big business. Your character can choose to fight by uncovering smut on the politician or by pointing out to the masses the crimes the politician has engaged in.
Few things are more fun to write about than the supernatural. Have your character rent a house in the desert for a weekend getaway. Let some old-timers tell your character a story of how a family just turned up missing one day, leaving the kitchen table with plates full of food. Let your protagonist laugh it off as she rents the house anyway, only to be awakened in the middle of the night by soft crying, laughter or screaming.