Joss Whedon is a member of the Unholy Triumvirate, which includes Aaron Sorkin and David E. Kelley. And he never, ever listens to the fans, who know much better than he does who belongs with who. Therefore, it is only just that the Mighty And Righteous shall come forth and steal his characters away and make them do mean nasty things with/to/on one another. But then they are quietly slipped back into his world, slightly sweaty and short of breath so the Humble but Righteous FanFic Author does not get sued by Joss, Mutant, Fox, UPN, or whoever else owns all the copyrighted material.
In plain english.. the majority of these characters, except where noted, are the property of Mr. Joss Whedon, Mutant Enemy, 20th Century Fox, UPN, Warner Brothers, and anyone else who pays for a little piece of the pie. All music belongs to various and sundry other people, most often MCA Records. All original characters are the sole property of the authors who created them. I have no money, I only do this for fun, please don't sue me.