i can't believe no one mentioned Joss Whedon's name. the writer/director of The Avengers, Cabin in the Woods, Buffy the Vampire Slayer (beats the shit out of anything else vampire related, with the exception of maybe Underworld), and I haven't seen much of Doll House but it's worth a look.
Bottom line, Firefly was one of his earliest and, short of Avengers, one of his best works, and honestly I still think it's better than Avengers in terms of hours of available content.
EDIT: ok someone did mention Joss Whedon explicitly, but seriously he's a far superior creator of film and television. He's a better writer, better director, works with more talented actors, AND HE JUST RE MADE MUCH ADO ABOUT NOTHING, AND IT WAS EPIC. Firefly was his origin, without it, we get no Avengers, or any of his future work that we'll still be talking about for years to come. who cares about JJ Abrahms? Did I spell his name right? never mind I don't care.