I had a random thought today. Does anyone remember the ABC comedies of the late-80s and early-90s? It seems that their entire comedy lineup crossed over with itself at some point. Family Matters was a spinoff of Perfect Strangers. Steve Urkle made a guest appearance on Full House. Michelle, Uncle Jesse and several minor Full House characters showed up in an episode of Hangin' with Mr. Cooper.
Just an odd thought about TV past, making me feel old now, too. 
Like the "Cosby Show" and "A Different World"
"Heathcliff" & "Garfield" - I'm not sure if this was an exact spin off. However, they did have similarities. Although, Heathcliff's mouth moved and was a junkyard cat.
Heathcliff, Tranformers, HeMan, Thundercats, & Silver Hawk were my favs as a kid.