To me, the question is, how do we define "surprise team?" Is it a team that we like to dis (see Colts) or is it a team that we don't like (see Chargers)? Or is it a team that most people truly don't think has any reasonable chance of winning the SB this year? After last season, when the Cardinals made it against very long season-opening odds, I think the definition of "surprise" has to be limited to teams with truly long odds.
Here is somebody's current list of the odds to win the SB, posted somewhere or the other (not presented as definitive or 100% accurate, but only as a place to start). I really don't want to argue about the finer distinctions among the top ten or so teams, but I just use the list to say, OK let's look at the teams that bettors now say are in the bottom half of this list (below the top 16 and ties), which starts with the aforementioned Cardinals in this case. I could look at any of the teams in the top portion of the list and say, hey, if a few things break their way, they could pull it off. I don't think it's likely that the Jests or Broncos, for example, will do it, but stranger things have happened. Atlanta, New Orleans with Brees, Carolina...they are all teams that could do it.
Looking at only the teams in the bottom half of the list, I'd pick the Redskins as the team with long odds against them, who might just do it. Their offense is suspect, but they have beefed up an already superior Defense and it's a truism that Defense wins Championships. Playing in the toughest division in football will harden them. If they get a few breaks (Romo implodes again, McNabb shows his age, Eli shows that his ring truly was a fluke) and get to the Playoffs, I could see them as the Surprise team.
But, they would be a very big surprise. Which is the question posed by the OP.
New England Patriots 8/1
Dallas Cowboys 9/1
New York Giants 10/1
Pittsburgh Steelers 10/1
Indianapolis Colts 12/1
San Diego Chargers 12/1
Baltimore Ravens 14/1
Tennessee Titans 16/1
Carolina Panthers 18/1
Philadelphia Eagles 18/1
New Orleans Saints 20/1
Atlanta Falcons 25/1
Denver Broncos 25/1
Green Bay Packers 25/1
Jacksonville Jaguars 25/1
Minnesota Vikings 25/1
New York Jets 25/1
Arizona Cardinals 30/1
Chicago Bears 30/1
Tampa Bay Buccaneers 30/1
Buffalo Bills 35/1
Houston Texans 35/1
Miami Dolphins 35/1
Washington Redskins 35/1
Seattle Seahawks 50/1
Cleveland Browns 55/1
Cincinnati Bengals 60/1
San Francisco 49ers 60/1
Oakland Raiders 75/1
St. Louis Rams 75/1
Detroit Lions 100/1
Kansas City Chiefs 100/1