Alan Alda didn’t have a major film career? How about Same Time Next Year, California Suite, The Seduction of Joe Tynan, and The Four Seasons, all released while he was still on MAS*H? He’s been in at least one or two movies a year, including Crimes and Misdemeanors, Betsy’s Wedding, and The Aviator. They haven’t all been starring roles, but most of them have been major supporting roles.
Ok, I get it. Sorry, my bad.
Cormac262:
Have to disagree - Most successful would be Kelsey Grammer, least would be George Wendt.
Rhea Perlman had a short-lived sitcom of her own called “Pearl,” don’t recall her doing anything aside from that, though.
I don’t know for sure but I’m guessing she’s semi-retired, having had a long and active active career. She’s certainly made enough during Raymond’s run and from rerun residuals that she’s probably doing more than just getting by. 
Oh yeah, completely forgot he was on the show! Don’t know who I’d pick as the more successful, but DiCaprio takes the edge due to being a regular cast member.
Remington Steele
Best career since: Pierce Brosnan (Steele) and Doris Roberts (Mildred Krebs) tied, I’d say. Brosnan had higher highs, but Roberts had a steadier paycheck.
Worst career since: Janet DeMay (Bernice Foxe), who has exactly 5 credits after leaving the show, only one of which was a recurring character.
To be fair, DeMay and done-much-better James Read were pretty much fired from the show.
Stephanie Zimbalist, who many people seem to think dropped from the face of the planet, has actually been pretty steadily employed and seems to work when she wants to.
Man, what was the deal with The Office? One or two of them did some voice work in a couple of animated films afterwards, and other than that nothing! Was that show a career killer or what?
“Happy Days”
Most successful: Ron Howard
Least successful: Either of the two guys who played Chuck Cunningham
Interestingly, the race for 2nd most successful looks like a competition between Scott Baio (post “Happy Days” highlights: starred in “Charles in Charge,” supporting role in “Arrested Development”) and Tom Bosley (starred in “The Father Dowling Mysteries,” supporting role in “Murder, She Wrote”). If we allow “dated an improbable string of hot babes” as an addition to Baio’s resume, then he’ll take silver, with bronze going to Bosley.
One that surprised me was Bruce Weitz. He played a popular character on the show and he seemed like a natural for at least the lead in another solid series (like Frantz for example). But his follow-up series bombed and his career stalled. He got work as a guest star but never became a regular much less a lead. He’s finally ended up working on a daytime soap opera which is usually where actors begin their career.
Not that I completely disagree with you, but do note that you have completely overlooked Anson Williams’ rather extensive career as a director.
I don’t know for sure but I’m guessing she’s semi-retired, having had a long and active active career. She’s certainly made enough during Raymond’s run and from rerun residuals that she’s probably doing more than just getting by.
Wow, 32 minutes between double posts. You got local temporal displacement, dude. 
This is a hard one: WKRP
Winner- Howard Hessmen, for a couple lousy parts in crap movies and sitcoms
Loser- Tied, Everyone Else! 
Well, to be fair, Mr. Carlson was the Maytag Repairman.
Here are two shows that have come back in one way or another.
Arrested Development (Luckily, almost the whole cast has kept busy doing fun things.)
Most Successful: Jason Bateman
For a while Michael Cera gave him a run for his money. But, I think Horrible Bosses probably put Bateman over the top.
Least Successful: Alia Shawkat
She’s mostly just had smaller parts, other than her return to the new season of AD. Which is a shame, because she is very funny.
Veronica Mars
Most Successful: Kristin Bell
Amanda Seyfried has been in some major league big things. But, I don’t think she has reached quite the height of popularity that Bell has.
Least Successful: Teddy Dunn
Lots to choose from, but he jumped to my head first.
I never watched the show, but I believe Adam Scott played a bit part, and now he’s gone on to do awesome things.
I don’t know. Ratzenberger’s movies have grossed more than 8 billion dollars! Mostly due to his work, probably.
Am I being whoooshed? Or, are you perhaps thinking of a different show? The Office just ended this year, so it would be difficult to pick most successful or least. Even the original Office has Martin Freeman, and Ricky Gervais vying for most successful.
Tim Reid had a pretty good run in several sitcoms after WKRP, like Simon & Simon, Frank’s Place, Sister, Sister, That 70’s Show, and most recently Treme.
I dunno, Tim Reid/“Venus Flytrap” did okay, probably at least as well as Hesseman - Reid was a regular cast member on Simon and Simon, he was the dad on Sister, Sister, he’s had recurring roles on That 70’s Show and Treme, and has played many smaller roles in between, enough to keep working consistently.
What about Tim Reid?
Nitpick: Simon & Simon was not a sitcom.
And not to sound like a broken record, but Frank Bonner did quite well as a director for a while and seems to be picking it up again.
Nitpick: Alia Shawkat does not have small parts.
Or I’m just careless and stupid. :smack: