My students have always enjoyed reading short stories by American writers like Jack London, O. Henry, and Mark Twain. You can find a growing list of these short stories – from VOA Special English – here on Successful English. The American Stories are in the Online | Intermediate section of Successful English.
You can read the stories, listen to them, or – what I recommend – read and listen to them at the same time. The stories are arranged according to the level of difficulty – from easiest to most difficult.
I have marked stories that my students enjoyed the most with asterisks (*).
Enjoy!