Caprica to Melrose Place (2009)

Caprica was a prequel to Battlestar Galactica

Battlestar Galactica's pilot had a scene showing a Firefly class ship flying over

Weyland-Utani is a client of Angel's Wolfram & Hart and also the company that made some of the weapons used by Firefly's Malcolm Reynolds in the Battle of Serenity

Angel was a spin-off of Buffy the Vampire Slayer.

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

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