In Stay Tuned, at one point, Roy Knable (who was played by John Ritter) stumbles through a channel onto the set of Three's Company (as a nod to his career). Lookalikes of Chrissy and Janet enter, asking him "Where have you been?" This leads to Roy screaming in terror as he changes the channel.
8 Simple Rules had an extended parody of this show, where John Ritter's character took on the Mr. Roper role.
The Golden Girls: When Blanche and Rose give Dorothy the silent treatment after having a row, Dorothy mentions that she thinks she once saw Jack and Janet do the same to Chrissy.
The Fantasy Island episode "Big Dipper/The Pirate" has a minor character who wants to act out the Three's Company fantasy. He's living with five girls, not two, which Mr. Roarke says is due to inflation.
In the episode, “The one with the Sonogram at The End,” Chandler, Joey, Monica & Phoebe were watching Three’s Company in Monica’s apartment, leading Chandler to say that they were watching an episode where there was some kind of misunderstanding.
In the season 2 episode, “The One With Two Parties,” has Monica and Chandler trying to keep both Rachel’s parents (who are divorced, but have also shown up) from seeing each other. While they do that, Chandler asks "Quick! What would Jack and Chrissy do?"
In the episode, “The One Where Ross Hugs Rachel,” Monica and Chandler try to tell Rachel that they're moving in together (Of course, this meant that Rachel will have to move out). Rachel at first, was under the impression that the three of them would live together and sings the first line of the show’s theme song, followed by Monica singing the second line.
Full House: In "You Pet it, You Bought it", Michelle makes $221 by selling lemonade to some construction workers on a hot day. She ends up buying a donkey, which she names Shorty. Uncle Jesse singing the Three's Company theme song is what keeps Shorty calm and prevents him from running loose in the house, but he doesn't remember all of its lyrics. The rest of the Tanner family members do, though.
