Code of Vengeance to Scorpion

The character of David Dalton first appeared on Knight Rider, then spun-off onto Code of Vengeance.

Team Knight Rider was a spin-off of Knight Rider.

1. Dr. Jackson Roykirk invented both the earthquake machine that had to be defeated by Team Knight Rider and the Nomad robot that had to be defeated by the Star Trek crew.

A Klingon Bird of Prey was seen in a spaceship graveyard on Red Dwarf

In the Red Dwarf episode "Psirens", the crew of the Red Dwarf come across a space ship graveyard which includes a Weyland-Utani ship, connecting it with Angel.

Angel was a spin-off of Buffy the Vampire Slayer.

The X-Files? Cigarette Smoking Man and Buffy the Vampire Slayer's Spike both smoked Morley cigarettes.

Homicide's John Munch questioned The X-Files' The Lone Gunmen.

Law and Order and Homicide crossed over on four episodes

Hudson University is the fictional University where many Law & Order characters graduated as well as the location of F.I.R.E.S.T.O.R.M. On Arrow

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

Hetty Lange from NCIS: LA helped out the investigators from Scorpion on a case