This is mostly a fantasy post, since I already know that whatever reboot that is the works at present is not helmed by Joss, and the rights do not include any characters from the series, but come with me anyway, gentle readers, on this ride of reboot madness!
Buffy Summers played by Keke Palmer
Additionally, there was a lacking of prominent people of color in the Buffyverse until the last season.
Joyce Summers played by Regina King
I almost went with Angela Basset, but then remembered the AWESOMENESS that is Regina King. In this reboot, Joyce would play a bigger role, and though not a slayer, equally kick ass. Who better than Ms. King?
Willow Rosenberg played by Saoirse Ronan
Now, this is where I will surround the black lead with a majority white cast, and Ronan is mos def a heavy hitter in the acting world. Willow's journey goes from geek to goddess, with some "bad bitch" moment in between. I think Saoirse could cover all of those bases and well!
Xander Harris played by Andrew Garfield
I think he'd be perfect as Xander. I can't really put the why into words right now, but after seeing him in "The Social Network" and "The Amazing Spider-Man," I think Andrew could accurately depict the complexities and heart and earnestness that is Alexander LaVelle Harris.
Rupert Giles played by Hugh Laurie
I debated on who to cast as Giles--Jeremy Irons. Alan Rickman. Colin Firth. Clive Owen (too young and too sexy). I finally landed on Hugh, who I think can play up the dark undertones of Giles, and who would read best as "father figure."
Angel played by Shia LaBeouf
And not a clean shaven-Shia, but this scruffy, long haired version of him. I think he's a great actor, and he broods quite nicely.
Spike played by Joseph Gordon-Levitt
Did I choose him because I just want to see him strut around like he's the cock of the walk in a leather duster? Did I do this cause of my big, girly crush on him? Did choose him because I just want to see him in anything and everything? Maybe. But I also know that this dude's got big ass acting chops, and that is something that Spike needs.
Faith Lehane played by Chloe Moretz
She's on the younger end of the spectrum, but she blew me away in "Kick Ass." [Big Daddy and Hit Girl deserved their own film, and easily stole the show.] If she could pull that off as a little kid, I'd like to see what she'd do in another kick ass role now that she's older.
Other actors who could be in this film somewhere: Jesse Williams, Michael Cera, Michael Pitt, Tom Hiddleston (probably as Wesley Wyndham-Price), Idris Elba (the dead beat dad Hank Summers?), Nia Long, Hayden Christensen, Zoe Kravitz (Cordelia?), Emma Roberts, Hayden Panettiere, Xac Effron, James McAvoy, Thandie Newton, and a plethora of cameos from folks of the Jossverse.