Castle to Doctor Who (1996) [pilot only]
7 connections
Castle
Law & Order
Hudson University from L&O also appears as the home of various victims and crimes in Castle,
Homicide: Life On The Street
Law and Order and Homicide crossed over on four episodes
The X-Files
Homicide's John Munch questioned The X-Files' The Lone Gunmen.
Buffy the Vampire Slayer
The X-Files? Cigarette Smoking Man and Buffy the Vampire Slayer's Spike both smoked Morley cigarettes.
Angel
Angel was a spin-off of Buffy the Vampire Slayer
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.
Doctor Who (1996) [pilot only]