But tons of other material is out there, some of it barely noticed in the vast verbal ocean of Web sites, books, newspapers and other publications.
The presence of a file or a memo doesn't necessarily mean the subject was targeted for an investigation.
"Celebrity files can be tricky to understand," FBI historian John Fox said. "They can be collections of information gathered from other files ... Louis Armstrong is a good example of that. It would be incorrect to say the FBI investigated him."
The FBI won't divulge its exact number of files, but estimates are that it could total more than 6 million. The agency has long maintained that its era of surveillance for political purposes is over, reflecting changes that followed FBI Director J. Edgar Hoover's death in 1972.
The high-visibility memorandums are generated for a number of reasons: the notoriety of the requester, whether it's a top government official (former US president Gerald Ford) or a higher-profile Hollywood type (Sinatra); if the request could reveal improper FBI activities; and if the request comes from a scoop-seeking journalist.
One of the files' more entertaining aspects is the failure to distinguish between legitimate and slanderous sources. Gossip-column clips sit side by side with anonymous letters like the one ripping Gleason and Hoover for hanging around with Sinatra, who -- as his file showed -- had once volunteered to work for the FBI undercover in 1950.