90210 to Petticoat Junction

90210 was a spun off of Beverly Hills 90210

Brenda Walsh picks up a Morley smoking habit while in Paris on Beverly Hills 90210

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."

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

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

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!

Hi Honey, I'm Home!'s Lloyd was friends with Mister Ed

The Beverly Hillibillies? Granny appeared on an episode of Mister Ed (see below for more on The Beverly

Petticoat Junction was a spin-off of The Beverly Hillbillies. Petticoat Junction spun off Green Acres. All three shows crossed over numerous times.