Wonder Woman?
She has worked with Joss Whedon before, is young (they want an actress who isn't in her 30's) and *Greek*.
C.O.R has shown she can be a major badass if called for, too.
My last comment was about Charisma, not Alexa. I had mentioned earlier in this thread that there had been a rumor that Charisma was also being considered for the role of WW and I was responding to a know-it-all stating the rumor I read was false. I don't know if this is just rumor or not (and don't really care anymore), but both Charisma and Alexa have worked with Wheedon before, and as you point out, on the same show.
I don't think it will matter who they get to play WW as I'm betting the movie will suck anyway.
"There's a body bag with that scumball's name on it, and I'm doin' up the zip!" -- David Lister from Red Dwarf