Currently a free agent: Bobby Carpenter (he was tendered as a restricted free agent but will likely be an unrestricted free agent), Vinny Ciurciu, Landon Johnson, Ashlee Palmer (exclusive-rights free agent), Caleb Campbell (exclusive-rights free agent), Korey Bosworth (I think)
New to the team: Doug Hogue (he was picked by the Lions in the fifth round of the 2011 NFL Draft)
Linebacker is probably the position with the most uncertainty for the Detroit Lions right now. DeAndre Levy is the only linebacker returning next season that has a starting spot locked down, meaning two openings exist in the starting lineup. Ashlee Palmer, an exclusive-rights free agent, and Bobby Carpenter, a likely unrestricted free agent, could both compete for starting spots, but both need to be re-signed before that happens. The same goes for Landon Johnson, who is going to be an unrestricted free agent.
Aside from Levy, there are three linebackers under contract right now. One is Jordon Dizon, who Martin Mayhew said earlier in the offseason will likely not be brought back. Isaiah Ekejiuba is mainly a special teams guy, so it's not expected he will be competing for a starting job. As for Zack Follett, he is just trying to return to football after suffering a serious neck injury last season. Although he was cleared by doctors to sign a deal with the Lions, it's not clear if he will for sure be able to continue his career going forward. Even if he is able to, I have my doubts that he will be competing for a starting job.
The other linebackers that could be on the roster next season include Vinny Ciurciu, Caleb Campbell, Korey Bosworth and Doug Hogue. Ciurciu is a solid special teams player and can serve as depth at linebacker, so he could earn a spot for his versatility. Campbell is an exclusive-rights free agent that just returned to football last year, and he could potentially put himself in position to make the team with his special teams work. Bosworth is likely to be just a camp body if he ends up being on the roster (it's unclear if he has a deal or is a free agent). Finally, Hogue is a fifth-round draft pick and should be in the mix for a spot on the 53-man roster.
Need going forward?
This is really the first position featured in this series that has a big need going forward. As mentioned, two starting spots are up for grabs next season, and there is a very good chance they could be filled with players not even on the team yet. Stephen Tulloch and Stephen Nicholas are both players that have been commonly mentioned as possible free agent additions, and I like the chances of at least one of them being signed.
While the Lions are in very good shape with basically all of the positions on offense and the defensive line, linebacker is at the top of the list as far as needs go heading into free agency.