Everyone I know who has watched Firefly loves it and despairs at the fact that there isn't more to love. So I was very excited when I found out that Joss Whedon had collaborated with some other writers and illustrators to produce a few graphic novels that add to the Firefly 'verse.
There are four collected volumes under the "Serenity" title released by Dark Horse comics and they're all pretty great. One volume is an adventure set in the same time period as the television series, another bridges the gap between the series and the movie, another provides the back story for Sheppard Book (!!) and the last deals with some of the fallout from the events of the movie.
Of course I am not satisfied and still want more, but that's how I feel about almost everything Joss Whedon does.