Angel to Person of Interest
4 connections
Angel
Buffy the Vampire Slayer
Angel was a spin-off of Buffy the Vampire Slayer.
The X-Files
The X-Files? Cigarette Smoking Man and Buffy the Vampire Slayer's Spike both smoked Morley cigarettes.
Fringe
Fringe makes reference to The X-Files classification of files.
Person of Interest
In the pilot of Person of Interest John Reese's suspect Diane Hanson has emails numerous characters from Fringe