Have you ever read someone's fic and thought to yourself, "I wonder what happened between those two scenes?" or even, "Nice place to end the story, but here's what I think happened afterward"? Have you, perhaps, then written the scene in your head? Since it's another person's story, though, you don't dare actually write it down.
I'm hereby giving you all carte blanche to do this with my stories. Any of them. There are two caveats only: first, that it must not violate the spirit of the story (which includes the pairing or pairings); and second, that you post it here or at your personal journal rather than in a public comm at least until I've seen it.
Most recent fic is over on the sidebar, or you can use the 'fic' tag. LJ fic compendium is here, though I don't have the most recent stuff added yet.