Family Guy was one, any others?
Moonlighting was cancelled after one season and brought back after a fan campaign. I think Taxi was also canceled by one network and brought back on another network.
IIRC Doctor Who was never cancelled, but it was put on hiatus in 1989 to be revived in 2005.
Brian
I don’t suppose you’ll count the Star Trek animated series?
Babylon V switched networks for the fifth season.
WKRP in Cincinnati kind of shambled forth from the grave for a while.
Twilight Zone, Outer Limits and Laugh-In, too…
or the movies, or all the New Trek series? Or even the fact that it would have been cancelled after two seasons if fans hadn’t demanded it be brought back?
The Critic switched networks.
King of the Hill was recently cancelled and then renewed, I think.
JAG was dumped by NBC after one season, then CBS picked it up and ran it for about a decade.
Matlock found a couple of extra years of life on ABC after NBC dumped it.
Roswell was cancelled by the WB as its second season was drawing to a close. Katherine Heigl cut off all her hair when she heard she wouldn’t be playing Isabel Evans anymore. 
Then Fox studios got UPN to pick up the show, probably as part of a package deal for getting ‘Buffy’.
Come to think of it, Twilight Zone’s been resurrected twice.
Cagney & Lacey and Designing Women were both cancelled in their first seasons and brought back due to fan write-ins (that proved the Nielsens were wrong). I know there are other shows for this list.
What’s Happening! had a regrettable zombie show (What’s Happening, Now!) several years after cancellation. Without Mama & Dee it didn’t work.
Likewise the body of Sanford & Son was stolen from its marble vault, hauled up to Maine, buried overnight in an Indian burial ground, and came back as Sanford (without son, without Esther, without Grady and Bubba, with a stupid sideplot about a Beverly Hills millionairess in love with Fred, etc.). Sometimes dead is bettah…
Oh, and the most famous example (or at least most lucrative):
Baywatch, starring Parker Stevenson and David Hasselhoff, was cancelled by the network after one season. Hasselhoff got together a group of investors and brought it back in syndication (without Stevenson). The cancelled show became the most popular show on the planet and made Hasselhoff very very rich (and will soon do the same for his ex-wife).
Dragnet was cancelled in 1959, but Jack Webb brought it back as Dragnet 1967, which went off the air in 1970. A third version hit the airwaves in 1989 (with different characters) and a fourth in 2003. They were all about cops in LA, based on LAPD files (“The story you are about to hear is true. The names were changed to protect the innocent”). Versions 1, 2, and 4 had Joe Friday as the main character, and he was played by the same actor in the first two versions.
Get Smart was cancelled by NBC, but switched over to CBS.
The Dick Van Dyck Show was cancelled at the end of its first season. However, it got great ratings during summer reruns, so CBS changed their mind and renewed the show.
Battlestar Galactica was cancelled after one season due to its high production cost, only to be revived a year later in the form of Galactica 1980 , a series so universally reviled that many BSG fans refuse to acknowledge its existence.
“Moonlighting” was successful from the get go and renewed after its first season. However, new episodes eventually became so infrequent that it may have seemed like the show was cancelled and brought back.
Absolutely Fabulous ran from 92-94ish and came back for another season in 01.
Maverick was originally on ABC and starred James Garner and Jack Kelly in the late 1950s-early 1960s. After a couple of seasons Garner quit in a contract dispute and Jack Kelly soldiered on. Garner was replaced Rober Moore. The show died shortly thereafter.
After several one shot tv movies tried to revive the show, Garner reprised the character for a show that lasted one year on NBC in the early 1980s, Brett Maverick .
This is more of a Brittish thing to do though. I don’t think it was cancelled.
Fawlty Towers took quite a break between seasons as well.
Home Movies started out on UPN and ran for 5 episodes before it was cancelled. Two years later it came back on Cartoon Network and ran for several more seasons.
Actually, Ab Fab wasn’t cancelled, but Jennifer Saunders (who wrote the entire series) said she didn’t have any ideas left for new stories after the third season. Evidently, she thought of some new ideas in the interim seven years.
How about “the Brady Bunch”? Cancelled in (I think) '74, brought back as a legendarily reviled variety show in '78, brought back again in the early 80s (as the set-up for a spin-off featuring only Marcia & Jan), and brought back yet again as a very ill-advised drama series. That’s three times the show was revived, not counting the animated series (which ran concurrently with the original series) and the TV movies or feature films.