The New York Giants. Yes, they won the Super Bowl last season, and yes, they came into a frigid Lambeau Field and made the Packers look like also-rans and exposed Favre as an old man. But have you ever seen a team's chances as repeating fall apart so quickly?
Indeed, they still have Manning the Younger and Plaxico Burress to play pitch and catch, and a solid running game. But what beat the Pats in the Super Bowl was the Giants' pass rush. The rest of their defense was unremarkable. And that is gone, my friend. Both starting DEs are done for the season, in addition to the starting safety and starting linebacker who left in free agency. And those weren't just any old defensive ends-- Michael Strahan (retired) and Osi Umenyiora (on IR) were both totally dominant down the stretch. Combined with Justin Tuck, those guys created the best front four pass rush on the planet during their playoff stretch. Without that push, hoo boy, people are going to put up some passing numbers this season.
With no Strahan or Umenyiora, I think the odds are about even that the Giants even make the playoffs. Just goes to show-- in the NFL, when you lose a great player or two, the tide can turn very, very quickly.