The fact that not many people have heard of the Panthers' linebackers does not mean this corps doesn't deserve to be ranked just outside the big three.
Jon Beason is an excellent young middle linebacker and does everything asked of him well. He is extremely competitive and wants to be great, which is exactly what he is becoming. Thomas Davis entered the league as a safety but now is a full-fledged playmaker at outside linebacker and someone to account for. The Panthers also have good depth and some position versatility, which cannot be overlooked.
The Cardinals play a lot of 4-3 and 3-4 schemes on defense, so narrowing down their outside linebackers versus defensive ends is not easy to do, but they do have a plethora of these types of contributors. However, they lack a major difference-maker off the edge. Gerald Hayes isn't a well-known player, but he is very tough and a much better overall player than many realize. Karlos Dansby was Arizona's franchise player, but his performance this regular season didn't quite live up to that lofty billing. Still, his talent cannot be denied.