Escape Pod and its sister publication, Pseudopod, provide podcasts of science-fiction, fantasy, and horror stories. Right now Escape Pod's running a flash fiction contest, with the guidelines here.
The cool thing is that entries are being published in batches of ten on the Escape Pod discussion boards. Readers vote on their favorite three, and those go onto the next round. I spent some time this morning reading through the entries, and while the quality is wildly mixed, it's fun to see what other people have done with the same amount of words.
One of the things I like about flash is that they're quick reads, bite-sized morsels rather than an entire sandwich-sized story. The short form means that people have to make every word count, and there's an amazing array of strategies for doing so.
I know there's more entries to come - haven't seen mine yet, for one! I'm looking forward to having a steady supply of flash fiction for a few days.