How about The Dick Van Dyke Show?  And the Chuckles the Clown Dies episode of The Mary Tyler Moore Show vault's it onto the list.  Also Taxi (who can forget the Rev. Jim Ignatowski and Latke).  And an honorable mention to Leave It To Beaver - the last non-dysfunctional family in America!  LOL
 
And while not truly a sitcom, I've got to agree with Olie about the Stooges.  In fact, I have a theory that one of the differences between men and women is that in the DNA chain, men have the appreciate the 3 stooges gene.  Women are missing this one.  Instead, in the same place, they have the stop and ask for directions gene that us males lack!  nyuk, nyuk, nyuk, oh, a wise guy, huh?
 
Bill, tgo

How about an honorable mention for The Andy Griffith Show.  
 
We have cops like Barney here in Mesquite.

I'll second the Taxi, Stooges etc. Throw in The Abbott and Costello Show(canned laughter and all). Even though the Stooges weren't a sitcom, neither was Our Gang/Littles Rascals, but they were my favorites as well. And yes, I'm old enough to have enjoyed Sunday mornings/afternoons with East Side Comedy/Dead End Kids and Henry Aldrich serials.

Leo Gorcey and Huntz Hall as Slip and Satch - brings back memories.  
 
Who knows where this one comes from:  Twang your magic twanger, Froggy?
 
Bill, tgo

I propose and support ...'A position that is at once simple, yet complex; firm, yet flexible; and above all, fair to every Alembician.' (with apologies to) -- Les Nessman, WKRP in Cincinnati ...

I really enjoy the more recent HBO series Curb your Enthusiasm by Larry David. I think it's the funniest show ever. Larry David is brilliant!
 
Duncan

Barney Miller, if only for the first few bars of the openning theme.
 
Rick

ANDY;S GANG MR PANZER......

You got it Flax.  
 
Barney Miller had an episode where they discuss the stooges and how Curly was the obvious genius of the group.  Officer Levitt walks up and, trying hard to be one of the guys, says Shemp was my favorite.  One of the other cops looks at him and deadpans we have nothing to talk about.  Loved that scene.
 
How about the Laverne & Shirley where they get engaged to Eric Idle and Peter Noone and go to the pot party where they see Lenny & Squiggy dressed as Simon & Garfunkel looking for Mary Jane?
 
And, of course, one of the funniest shows that wasn't meant to be funny:  Dragnet.
 
Bill, tgo

i'm not sure if sitcom is the correct description but MASH has to be up there with the best. Others I really enjoyed were the MTM show and its spinoff, Rhoda. I was also into Happy Days, and Laverne and Shirley although what the current PC brigade would make of a 35 year old man luring teenage boys into the gents toilets is anybody's guess;-)  
 
graeme

Gee ... a lot of good picks! Scrubs is great ... Police Squad was awesome too. I think one of my favorites was Seinfeld ... The Master or your own Domain program. The one where they all made a money bet to see who can go the longest without ... ammm .... (don't let the kids read this) masturbating ... and one by one they lost. Funny as is gets! Not to mention it was such a taboo subject on prime time TV! :-)

Anyone remember Key West? I looked For many years for for the videos of this one,My daughter found the entire 13 episodes somwhere on the net and gave them to me last christmas.Great series,sort of a southern version of Northern Exposure.
 
Chuck

The Simpsons are the greatest sitcom of all time.  I can't believe no one has mentioned them.

Till the day I die, 'I Love Lucy', the Three Stooges, and the Our Gang/Little Rascals, ALWAYS make me laugh no matter how bad my day's been.  And the b+w 'Andy Griffith' episodes.  Then when I wonder what it would have been like to take drugs, 'Green Acres' and 'Get Smart'.
 
J o e y

Does anyone remember Hello Larry?   I loved that show.