Do you like or not? What are your favorites?

The Nanny: "Imaginary Friend"

Green Acres, "Charlie, Homer, and Natasha." Eb has an imaginary friend named Charlie.

Here are a couple of sitcom episodes with imaginary friends:
In an episode of Gimme a Break, Samantha mentions an imaginary friend named Debbie Jo.
A Family Affair episode centered around Jody having an invisible bear named Arthur.

"Imaginary Mary" was an entire series which only lasted for a few episodes starring Jenna Elfman of "Dharma and Greg" as a woman who had an imaginary friend that she has known since childhood.