Deadline to Melrose Place (2009)

Characters from various Law & Order series have read, referenced or visited the offices of the New York Ledger, the fictional paper from Dick Wolf's series, Deadline.

Law and Order and Homicide crossed over on four episodes

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

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

90210 was a continuation of Beverly Hills 90210 years later

Melrose Place (2009) was a continuation of Melrose Place which was a spin off of Beverly Hills 90210 that was continued as 90210