There are many, many more that are favorites for a few months then it's off to another sitcom (thanks to Netflix, Blockbuster online, and the other internet outlets - no more waiting for DVDs in the mail!). These three are my most memorable favorites. If there was a fourth - it would be The Simpsons, who have supplied most of my avatars.
Honorable Mentions:
Home Improvement
The IT Crowd
The Addams Family
The Munsters
Get Smart
MASH
All In The family
Hogans Heroes
And, really, Top Gear should count as well.
My favorite "old" sitcoms were The Honeymooners, Sgt. Bilko and the Dick Van Dyke show.... They would be on when I got hone from school in the early 80's
On The Buses
Bless Me Father
Man About The House - original UK version of Three's Company
Monty Python's Flying Circus (OK Python is not a SitCom,, but damn funny!)