A lot of the ones mentioned already, especially MST3K.
I also have to admit that I fell out of my chair laughing at the first few episodes of My Big Fat Obnoxious Fiance.*
*I’m so ashamed.
I forgot about MBFOF. That show made me laugh. As did the never-finished spinoff My Big Fat Obnoxious Boss. And I’m not ashamed either.
Thanks everyone! There are a lot of great shows that simply slipped my mind…And thanks to Pokey for reminding me of my ALL time favorite show, Kids In The Hall . (Gah! How could I have forgotten that one??) Plus, The Office (BBC), Fawlty Towers , Conan O’Brien ,Will and Grace…And some that I haven’t seen that I will have to check out!
Since I’ve been pregnant I’ve been a weepy, pathetic mess (ahh hormones) - so I think I need to watch more funny shows. Laughing really is good medicine! 
I want to second Ally McBeal since it’s only been mentioned once. I’ll add Fawlty Towers and Three’s Company which I don’t think were in previous posts. Also, the aforementioned:
Futurama
The Simpsons
Family Guy
Frasier
Scrubs
Monty Python
SNL
Dave Chapelle
And, as I discovered last night, Benny Hill.
Some of these were mentioned earlier, which I’ll add my votes to:
British:
Yes, Minister and Yes, Prime Minister
Fawlty Towers
Absolutely Fabulous
Coupling (which I’m watching as I type)
American:
Frasier - particularly the first couple of seasons - season 2 had the episode where the Crane brothers decide to open a French restaurant that was screamingly farcical
Buffy
Northern Exposure
Mary Tyler Moore - some episodes - think Chuckles the Clown “shelled” by an elephant
Mad About You - the thanksgiving episode with all the turkeys
The Daily Show
Canadian:
This Hour Has 22 Minutes
Made in Canada - I wish it would come out on DVD
Rick Mercer’s Monday Night Report
Talking to Americans
and lest anyone think I don’t find anyone funny but Rick Mercer - Corner Gas
Hmmm…one that hasn’t been mentioned yet but (to me) was incredibly funny, including one of the single funniest episodes of anything I’ve ever watched, is News Radio.
Oh, the episode was the Super Karate Monkey Death Car or whatever it was called.
Oh good, I really fit in here!
Kids in the Hall
The Young Ones
Monty Python
Futurama
Newsradio
Third Rock from the Sun
The Office (BBC)
And…Trailer Park Boys!
Is that on DVD yet?
Family Guy
Sealab 2021
MXC
America’s Funniest Videos
The 700 Club
Yes it is. Enjoy.
Definitely Strangers With Candy. That show was pure genius. I used to watch it every day because my (ex) boyfriend had all the boxed sets. Almost makes me want him back!
Also: Freaks and Geeks. Bill was the man! “You like to pat boys’ butts, you butt-patter!”
And anything on Adult Swim, including but not limited to: Aqua Teen Hunger Force, Sealab, Home Movies, and Family Guy.
King of Queens regularly has me laughing also. I think it’s the funniest sitcom on the air right now.
Friends also never fails to crack me up. I think its one of the very few shows that is consistantly funny.
Corner Gas
Being Saskatchewan for all my life, I never realized how funny we are
I’m not a big “laughing out loud” person when it comes to television shows, movies and the like, but the following have elicited a hearty giggle from my stoic lips on more than one occasion:
Kids in the Hall
Space Ghost
Aqua Teen Hunger Force
Twin Peaks
Chobits (really. I’m that juvenile)
Ijust have to second Coupling. Geniously hilarious, I say.
The first show that I recall to have me LOL alone whas Who’s the Boss.
The Tick
Duckman (But the time travel episode had me crying real tears)
Arrested Development
Strangers With Candy
Pete and Pete
No one has mentioned Mr. Bean or Blackadder yet? Rowan Atkinson makes me laugh out loud.
My top three are:
Family Guy
Frasier
Futurama
Wow, they all start with ‘F’. Hmmm…