Arrow to The Art of Being Nick

Hawaii Five-O references Dominic Alonzo from Arrow

NCIS: LA and Hawaii Five-O worked together in a crossover episode to stop a smallpox outbreak

NCIS: LA was a spinoff of NCIS

NCIS was a spinoff of JAG

Oceanic Airlines

Mannix returned to TV on an episode of Diagnosis Murder to solve an old unsolved case with the help of Dr Mark Sloan.

Here's Lucy's Lucy Carter and Mannix's Mannix are held hostage in an episode of Here's Lucy.

Here's Lucy's Mary Jane Lewis was originally a character on The Lucy Show (also called The Lucille Ball Show).

Mr. Mooney from The Lucy Show was on Hi Honey, I'm Home!

Leave it to Beaver's June Cleaver crossed over onto Hi Honey, I'm Home!

Eddie Haskell from Leave it to Beaver appeared on Parker Lewis Can't Lose

Andrew Keaton from Family Ties appeared in an episode of Parker Lewis Can't Lose

Family Ties had a failed spin off called The Art of Being Nick focused on Mallory's boyfriend Nick Moore.