Penny Stock

Don't forget Jetsons meet the Flinstones ;)

I am not sure about this one but Brandy -> The Parkers. I was never a big fan of either but I have seen many of the same character on both.

oh wait, the show was called Moesha, not Brandy. Here is another one, i think, Buffy -> Angel. And how about all the Law & Order shows and the CSIs? how about Star Trek?

All in the Family also spawned Maude and, I suppose, 417 Hauser (or something like that)
Star Trek Spawned the Next Generation, Deep Space Nine, Voyager and Enterprise
Cheers also spawned a (very) short lived spinoff based on Carla's husband and his new family.
Lou Grant was spawned by Mary Tyler Moore.
Law and Order has spawned a variety of spinoffs.
(Homicide may get partial credit for spawning Law and Orer:SVU as the character of Det. Munch played by Richard Belzer was spun to the newer show when the former one was cancelled. Belzer might now have the title for longest tenure as a single character now that Kelsey Grammar is leaving.)
CSI has spawned CSI:Miami and an upcoming spinoff.
And let's not forget that 21 Jump Street spawned Booker.
(It could be said that the Tracey Ullman show spawned the Simpsons. I guess the cast of the Simpsons realistically have had their roles the longest. But they're cartoons.)

Well done all. Keep em coming! I am still unsure about the CSI's, Law and Orders and Star Treks. I know they were spawned from one another but were (are) there any common characters? Just curious. I was thinking Maude came from something I just didn't know what...

Well Dr. McCoy made an appearance on the pilot of The Next Generation 18 years (real time) after the original Star Trek ended. Commander Sisko was ferried by the Enterprise to Deep Space Nine. And Voyager's last mission in the Alpha Quadrant was launched from Deep Space Nine. If Enterprise has any such connections to the previous shows I have no idea.

Occasional characters crossover among the different L & O's.

Oh and with the Practice ending it is spinning off a new show that, I suppose, is to be the new Ally McBeal. Or at least an oddball Boston law firm.

David- I bow to your superior knowledge of all things Star Trek!

I think we decided that a spinoff must take existing characters from a show and "spin" them off into a new show. Thus, Fraiser is a spinoff, since the character of Fraiser Krane was integral to both shows. The Star Trek examples, however, were simply borrowing from the genre; the characters from the preceeding series did not actively play a role in the new series. That would be considered a cameo, not a spin off.

Looking at your list, and the comments above, I have a few to add:

Mary Tyler Moore, in addition to Rhoda and Lou Grant, also spawned Phyllis.

Happy Days spawned a very short lived show called "Out Of The Blue", and an even shorter lived show called "Blansky's Beauties" (and, Happy Days itself was actually a spin off of an episode of Love American Style).

All In Family I think can also be credited for Good Times, which in reality is a spin off of Maude, which was a spin off of AIF. AIF also spawned 704 Hauser Street, which had a Black family living in the home once owned by the Bunkers, and starred John Amos (post Good Times). Archie Bunker's Place, was also a spin off, though some would argue it was actually a continuation of AIF.

To add another - Dragnet begat Adam 12, which begat Emergency.

You're good!