The Legal Times reports that the states supporting the video game industry's side of the Supreme Court fight include Utah, Rhode Island, Oklahoma, Washington, Georgia, Arkansas, Nebraska, North Dakota, South Carolina, and the wonderful territory of Puerto Rico. You can grab that brief here (Thanks again to our Shoutbox hero BearDogg-X).
The brief was written by Rhode Island Attorney General Patrick Lynch and supported by Irell & Manella in Los Angeles. The main argument of states supporting the industry is that the California law is an overreach, against First Amendment freedom, and puts an undue burden on law enforcement, who have better things to do. The brief also points out that the law opens up the possibility of criminals using the defense "video games made me do it."
The blog points out that both Lynch and Utah Attorney General Mark Shurtleff received campaign contributions from the Entertainment Software Association. The point has been noted elsewhere, but this particular blog likes to report on lobbyists efforts.