In "A Blast for Buck", Legion of Death leader Kellogg is on the long list of suspects who may have sent the deadly riddle. Appropriate as Kellogg was played by Frank Gorshin, who once played a Riddler.
The Other Darrin: Bob Elyea as Twiki's voice in the second season. Also, Kane was played by Henry Silva in the pilot movie and by Michael Ansara in the series proper. In both cases, the cast changes came with a personality change. Twiki became more grumpy and cantankerous. Kane became honorable and dutybound.
Prop Recycling: The Earth starfighters were a draft design for the Colonial Vipers from Battlestar Galactica; Buck's shuttle Ranger 3 and the stock footage of New Chicago were recycled from Galactica's "Terra" arc. At one point in the Pilot movie, a closeup of the Earth starfighter's joystick is identical to the 3-button joysticks in Galactica (later episodes use a different joystick prop).