The King of Queens was the last live action sitcom starting in the 90s to end its run, running from 1998-2007.
Descended Creator: Nick Bakay, who voiced Salem, was a writer for the show and also did several uncredited voice-overs in many episodes. He began to appear onscreen in later episodes.
Title Sequence Replacement: The first season's opening just showed a brief clip of a subway going by. It wasn't until season 2 that the "Baby, All My Life I Will Be Driving Home To You" theme (and the clips it was set to) started.
Keep Circulating the Tapes: Starting in the fall of 2007 (some months after the show ended) reruns of the show started using a shortened version of the "Baby, All My Life I Will Be Driving Home To You" opening, making the original a rarity that those who have caught the show in reruns will likely be surprised to discover.
The Other Darrin: Deacon's son, Kirby Palmer, was played by three separate children over the course of the show.
The same goes for Deacon's younger son, Major, who was also played by three children.
To be fair, though, this is the only way a show not structured as Real Time can continue to show young children.
Also, when Spence's mom Veronica first appeared in "S'Aint Valentines", she was played by Twin Peaks star Grace Zabriske (as Anne Meara was playing another role in that episode). By her next appearance, Meara had taken on the role and would play it for the rest of the series run (Anne Meara was Jerry Stiller's Real Life wife, which is played with later on when the pair flirt and date).
Doug's Boss, Supervisor O'Boyle was played by Sam McMurray throughout the entire series, except for Season 1's "White Collar", where the character was played by John F. O'Donohue. The character's name is given as "Jack" in the credits but McMurray's character's first name is Patrick. While the fact that Doug could have two supervisors with the same last name is not completely impossible, a later episode centered around a flashback to when Doug first started working at IPS (season 8 episode "Consummate Professional") has the McMurray character as Supervisor.
Also Carrie's Boss in Hornstein & Steckler, Mr. Kaplan, was played by Victor Raider-Wexler. When Carrie eventually gets a job at a Real Estate Firm her new boss was played by the same actor.
You Look Familiar: Leah Remini's real life husband, Angelo Pagan, guest starred six times as five different characters on the show.
Also, Kevin James' real life wife, Steffiana De La Cruz, guest starred five times as five different characters.
The king (no pun intended) of this was Mookie Barker, who guest starred in many episodes, almost always as a different character.
Chris Elliott played "F. Moynihan" a customer of Doug's in one episode and as a wacky exterminator several seasons later.