For those times when flash fiction just takes too long to read, check out Thaumatrope, which features Twitter fiction (140 characters or less) for readers of sf, fantasy and horror. The stories are like potato chips--you really can't sample just one.
The site publishes serial fiction too, and it's even fun reading the bios of the writers and seeing what they have in the pipeline. My favorite is Robert T. Jeschonek, whose upcoming Clarion YA novel is called My Favorite Band Does Not Exist.
Thaumatrope is now one of my favorite sites for dropping in for a few minutes of entertainment (along with Fark).