It has been one week since the NFL free agent frenzy began, and most of the big name players have signed with their new teams. There were some big surprises, some questionable trades, and some under-the-radar signings around the league.
Obviously the addition of Nnamdi Asomugha was a major factor in deciding one of the teams that made this list. There were some teams that didn't even really make any significant moves on defense, but are still considered one of the best.
As we look forward to getting the preseason started in less than two weeks, it will take time for teams and players to put it all together. There is going to be some sloppy offensive play in the first few weeks, where defenses will dominate. As the season goes on, these five teams will continue to shut down opposing offenses.