The NFL, more then any other league, embraces parity. In any other preseason when teams begin to assemble and talk about this "being their year", most teams know they have little to no true shot at the championship. I don't think the Kansas City Royals were booking October hotel rooms in spring training.
However, this is the NFL, where it's not unheard of for a team to go from awful to playoffs without anyone expecting it. Just take a look at the NFC South division since it's existence:
2002: 1st - Tampa Bay (12-4), Last - Carolina (7-9)
2003: 1st - Carolina (11-5), Last - Atlanta (5-11)
2004: 1st - Atlanta (11-5), Last - Tampa Bay (5-11)
2005: 1st - Carolina (11-5), Last - New Orleans (3-13)
2006: 1st - New Orleans (10-6), Last - Tampa Bay (4-12)
2007: 1st - Tampa Bay (9-7), Last - Atlanta (4-12)
All except one year, the last place team from the year before won the division the year before. Now, I am in no way predicting an Atlanta divisional victory. However, the Browns (+6 wins last year), Saints (+7 wins in 2006), and Bears (+6 wins in 2005) all show it's a league wide epidemic.
The perfect storm of youth, experience, emotion and quiet breakout stars all come together to make the following teams this year's candidates for the team we're all talking about.
St. Louis Rams (3-13 in 2007)
This team is still stockpiled with talent on offense. Steven Jackson, Marc Bulger, and Torry Holt are one of the best tandems in the entire NFC when healthy. While there are issues with all of them (Jackson's contract, Bulger's health, Holt's age) they are still electric if they can get on the field at the same time. Their problem last year was obviously the defense, as it allowed the 2nd most points per game (27.4) in the NFL. With Chris Long joining up, they should be able to improve on their pass rush. If their big three stays healthy and their defense can cut the opponents scoring to at least an average, they could easily flirt with .500 which is playoff borderline in the mediocre NFC.
Baltimore Ravens (5-11 in 2007)
It's tough to put stock in any team that looks like a rookie QB will be their starter, but the Ravens were right on the cusp last year even with Kyle Boller taking most of the snaps. Baltimore was a very respectable 4-4 at home which means, do the math do the math, 1-7 on the road. Even with tough road match-ups against Dallas, Indianapolis and Pittsburgh, they have very promising match-ups at Houston, Miami, and the New York Giants. If Flacco performs half as well as people are praising him in camp, the Ravens will be right in the wild card mix.
Buffalo Bills (7-9 in 2007)
I don't think they're anywhere near ready to overtake the Patriots in the AFC East. But I do see them improving dramatically. They completely overshot what they deserved record wise last year. With no real solidified starting quarterback, dozens of players on the injured reserve, and the toughest schedule in the league, they stillcontrolled their own playoff destiny up until Week 16. If they stay healthy, finally have an established starting QB for the length of the season, and open up the offensive playbook, they can quickly become a team to reckoned with on both sides of the ball.
Look also at my Candidates for the Disappointing Teams of 2008.