I think you'd know what team I'd pick as a candidate to go the longest. (see screen name)
However, it's really hard to believe that any NFL team could go 0-16 in this era. In the "old", pre-free agent days, when you built your team almost solely through the draft, if you had a few bad draft years, it would take seemingly forever to recover. Once you got to the top, it was easier to stay there, hence, the dynasties of the Steelers, Cowboys, Packers, and that team by the bay. Therefore, there were more really good teams, and there were more really bad teams. A larger span in team talent from top to bottom, if you will. And if you were an expansion team in those days (like the Bucs) it's easy to see how they would struggle for so long out of the gate.
Today, you can go from 3-13, to 13-3 in one year and win the Superbowl (and we ALL know who I'm talkin' 'bout). :l Parity is here to stay, like it or not. It's really true today that any team can beat any other team on any given day. So what I'm getting at is that a very bad team like, let's say.... the Raiders, unlikely won't lose every game. One or two games this season, the other team will play down to the talent across the line, all the breaks will go the right way and the ****ty team will win. Kinda like what happened to the Rams in Whinerville
That being said; even though the Bucs and Lions haven't won yet, they're not that bad, as Bruce=Goat said. The Titans, I think, are a notch above the Raiders in talent too. They're just too young right now. The Raiders though... they have set a new standard in bad. They have put together a team and coaching staff that will take years to recover from, even with free-agency. However, they have the Whiners and Texans on the schedule, so anything can happen.