Emilio Estevez (Charlie Sheen’s real-life brother) appeared on an episode of Sheen’s sitcom, “Two-and-a-Half Men”.

  Suzanne Pleshette, who co-starred with Bob Newhart as his wife on his sitcom “The Bob Newhart Show” from 1972 to 1978, also appeared on the last two minutes of the final episode of his next sitcom “Newhart” (1982 to 1990). The plot device had Newhart back in his apartment from the earlier sitcom wake up in the middle of the night and awaken his wife next to him, who turned out to be Pleshette. He told her that he had had a strange dream that he was the owner of an inn located in rural Vermont and married to a beautiful blonde woman who always wore fashionable sweaters. All of that was the setup of the current series.

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  Denise Richards, Charlie Sheen’s real-life ex-wife, appeared as a guest star on his sitcom, “Two-and-a-Half Men” as one of his numerous ex-flings and/or ex-girlfriends. 

  I believe that his father, Martin Sheen, also appeared on that series at some point. 

  At least a dozen celebs appeared on Seinfeld”, at least baseball players, I believe one was Alex Rodriguez, the former mayor of New York City Ed Koch, actress and singer Bette Midler, etc. 

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• "The Nick of Time" 1960: A honeymooning couple stops at a diner that has fortune telling machines at each table. Shatner's character begins to believe that the machine is really telling the future.
• "Nightmare at 20,000 Feet" 1963: On an airline flight, Shatner's character is the only one to see a gremlin on the wing of the plane tearing at the engine.