Shawne Merriman, at just 26 years old, may well have something left in the tank.
While he may never be the pass-rushing force he was from 2005-2007, some teams can still use his services. If utilized correctly, Merriman can be turned into a situational pass rusher or an ordinary down-lineman. It all depends on what coach gets hold of him and attempts to mold the second part of his career.
With his 6'4" 265-pound frame, Merriman could land on a team with an aggressive defensive coordinator that unleashes him on obvious passing downs, or his coaches could have him focus on fundamentals. Luckily for Merriman, he is the right size to play either outside linebacker in a 3-4 or defensive end in a 4-3.
Though all five of these teams do not share a base defensive scheme, they all share two traits: a lack of a pass rush, in general, and more importantly, lack of a pass rush from positions where pressure on the quarterback traditionally comes from in those schemes and an inability to stop opposing team's running games. So no matter what the scheme or what the coaches ask Merriman to do, all five teams can definitely use his services.
Merriman must first get completely healthy, however, because he will be no good to any team if he can't stay on the field.