One of NBC's longest-running programs, this seminal game show was a daytime staple from 1958 to '73, with forays into prime time in '58 and '61. Of all the emcees who revealed the rebus (Ed McMahon and Bob Clayton among them), Hugh Downs is the one best remembered. In 1987, the series was resurrected as 'Classic Concentration,' with Alex Trebek as host until the show's end in 1994.