5. Frank & Estelle
George Costanza's parents were so memorable, that I always thought a spin-off featuring these two high strung senior citizens finally moving down to Florida would have made the perfect sitcom. We pretty much only saw Frank and Estelle Costanza when their lives converged with George's, and a spin-off would have given us greater understanding of the turbulent chilhood of George, as well as seen the often angry couple adjust to life in the Sunshine State. The elder Costanzas moving to Florida would have been the perfect way to avoid any issues of lack of interaction with the core of the Seinfeld group, but given Jason Alexander plenty of opportunities to reprise his role in a believable way. Perhaps he'd come visit to celebrate Festivus every year.