I know of only one.

1.15: "Dead or Alive", which was a script that was written and subsequently discarded for the series. Instead, they took elements (and lines) from this and plugged it into other episodes.

For some reason, this is refusing to let me link to it directly. But you can find it here: http://www.fanpop.com/spots/firefly/links/4244496

It isn't exactly an episode. But I remember seeing the original 130+ page script Joss wrote for Serenity which includes quite a bit that isn't in the movie.