According to Pro Football Talk, the Cincinnati Bengals currently rank fifth in the NFL with $16.58 million available under the team's salary cap for 2012. Jacksonville ($25.1 million), Tennessee ($19.97 million), Philadelphia ($18.02 million) and Cleveland ($17.7 million) round out the top five. During the last public release of the team-by-team salary cap, the Cincinnati Bengals had roughly $19.1 million under the cap, third behind Jacksonville and Philadelphia at the time.
And since that time, without going into great detail, the Bengals signed a chunk of undrafted free agents along with nine of their ten rookies selected during the 2012 NFL draft. Additionally Jacob Bell retired from the NFL and the team also released/cut a handful of college free agent signings before the first week of OTAs due to failed physicals. All of which supposedly accounts for the team's 2.5 million-plus decrease against the cap.
However don't expect the team to sign any high-profile free agents just because they have money available. Along with the need to sign a handful of players to eventual extensions, and the team's somewhat public impression of being satisfied with the roster as it stands, the Bengals like to set aside money for in-season surprises -- such as injuries -- which require additional signings.