Niel DeGrasse Tyson? I don't know his position on SOPA, but I'd imagine he's against it. John Hodgman? He's a writer for Wired, been on Diggnation, Attack of the Show, and TED, and works with Jonathon Coulton. He's got a ton of 'net-cred and is frequently on TDS.
I would much more prefer seeing one of the household names in the "old" media see speak out - some of the more expected opponents like Al Gore, Mc Hammer or Aston Kutcher would give the issue a better face and show that the opponents are not just some people from the internet who want to "to kill our beloved music and movie culture".
