Sam Montgomery, DE, LSU: Cincinnati ranks near the top of the NFL in sacks, but most of that production is coming from inside (Geno Atkins) and Michael Johnson is set for free agency next year. Montgomery has a few question marks, but there is no doubt about his combination of athleticism and strength to create pressure in the backfield.
Michael Johnson is indeed set for free agency and if the Bengals are unable to re-sign him, they would need to bring in another defensive end to replace him. Carlos Dunlap is likely going to take over the starting role at the opposite defensive end for Robert Geathers, who is also a free agent, and losing Johnson would be a big blow to the defensive line.
Even if the Bengals do re-sign Johnson, bringing in another defensive end that is able to get pressure on the quarterback from the edge may not be too terrible of an idea considering you can never have too many good pass rushers. However, there are larger holes to fill, such as the one at strong safety, the one at linebacker and possibly one on the offensive line, if the Bengals aren't able to re-sign Andre Smith.
The bigger question is if the team has learned from not being able to re-sign Johnathan Joseph or not.