For 2009 the answer was the Detroit Lions (2-30 for two seasons) and the St. Louis Rams (1-15 for one season). The newest team, the Houston Texans, had a franchise record of 49-79 (2002-2009).
However, by 2011 both the Lions and Texans had vastly improved, and the weakest teams appeared to include the Rams, the Miami Dolphins, and the Indianapolis Colts who were without Peyton Manning (in his 13th year). Both teams did better in 2012.
In 2012, the worst record belonged to two AFC teams: the Jacksonville Jaguars and the Kansas City Chiefs.
(see discussion for previous answer)
In 2008, the Detroit Lions became the first ever NFL team to finish with a 0-16 win-loss record. So, some would consider them one of the worst if not the worst.
tennessee titans
washington redskins
The Detroit Lions.
Bad offense They won super-bowl XLIV, maybe?
The Cleveland Browns. They are also the worst team because they don't have any good players.
bears
There is not a chance in the whole world that the best college team beat the worst NFL team!
Lions
As of November '09 the St. Louis Rams are the worst team.
Cleveland Browns, and BENGALS
The NFL team with the worst overall record in 2008 was the Detroit Lions, who were 0-16.
the browns or the jaguars
Raiders
tennessee titans
Indianapolis colts
The Dallas Cowboys
The Houston Texans.