It's still very early, but Las Vegas sportsbooks have been handicapping 2013 Super Bowl odds for a while now. The St. Louis Rams opened at 200/1--as did Tampa Bay--and those were the worst odds in the league. Since then, however, the Rams' odds have improved to 40/1 at some sportsbooks.
Those odds place the Rams ahead of seven other NFL franchises, though they're always subject to change. Grantland's Bill Barnwell offers an extensive breakdown of the latest odds from the MGM family of sportsbooks.
The San Francisco 49ers have the best Super Bowl odds at 4/1, followed closely by New England and Green Bay at 6/1.