Hanging In to Space: 1999

Hanging In (and Maude's) Maggie Gallagher crossed over onto Soap for 10 episode

The first All in the Family spinoff character was Maude. Maude was Edith Bunker's cousin.

The Jeffersons' George Jefferson was the second All in the Family supporting character to spinoff onto his own show.

George Jefferson gets help from Barney Collier from Mission Impossible

Mission: Impossible was continued 22 years later

Diagnosis Murder's Doctor Jesse Travis's father is a spy that someone is trying to kill. One of the possible suspects is the original Mission: Impossible's Cinnamon Carter.

The airplane that crashed and strand the cast of Lost was Oceanic Airlines Flight 815 also featured on Diagnosis Murder.

In an episode of Veronica Mars, Veronica's fortune cookie had the numbers that won Hurley from Lost the lottery.

The mugshot of Malcolm T Wiggins from the X-Files episode "Titonus" appears on the wall of a police interrogation room in the Veronica Mars episode "Leave it to Beaver." Also the fictional car rental company Lariat where Mulder & Scully always rented their cars was featured prominently on the Veronica Mars episode "Rat Saw God."

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

Angel was a spin-off of Buffy the Vampire Slayer

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.

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 Space: 1999.