Top of my head:
The Mary Tyler Moore Show.

Barney Miller- the only long-running series in history that won an Emmy for best comedy in its final season without having won the best comedy Emmy before. While not quite as good as when Yemana was still alive, season 8 was still a very solid season.
Happy Days- Season 11 was an improvement over season 10 because Joanie was back.
M*A*S*H- I know a lot here hate the later seasons. But while M*A*S*H had some clunker episodes, every season was good in my book.
Frasier- While not on the level of the fantastic first six seasons, season 11 was an improvement over 8 and 9, which are easily the weakest two from the series. (Season 10 I liked because of Millicent Martin being a regular.)
Seinfeld- I also don't think this show suffered when Larry David left. Plus the series finale so many hate I like.
Wings- While it lost a step with Lowell leaving, Wings remained funny throughout the whole run.
Growing Pains- Season 7 was one of my favorites with Luke being a regular.
Green Acres- Weakest part of this was easily in the beginning. Green Acres stayed consistent once it became good.
White Collar- a short final season but it was still good.
Monk- Any Natalie season beats the Sharona era. Plus the series finale was fantastic.
Coach- I like the Orlando era with Katherine Helmond. And that location was also Tim Conway's only appearances, he was great on Coach.
I Love Lucy- I am referring to season 6 here. Technically The Lucy-Desi Comedy Hour was a separate show, although I can see fans putting both shows together.
Adam-12- great show the whole run
3rd Rock from the Sun
Reba- It is too bad the CW hated this show. Reba was still good creatively for season 6, and even buried Sundays at 7:30 got better ratings than their Monday comedies. Plus Scarlett Pomers was gorgeous in her return.

Agree about Seinfeld.

I thought the final season of Perfect Strangers was very good, although it was very short.

I liked the final season of Who's The Boss because we got payoff with Tony and Angela finally together as opposed to hooking up in a finale or something.

Modern Family's final season was well done.

Also, Facts of Life, Night Court, Cheers and Alice

Happy Days- Season 11 was an improvement over season 10 because Joanie was back.

Yeah, I noticed that final season was decidedly different from the others. It seemed like a return to the more adult first two years. Stories dealt with drug abuse, attempted rape (of Joanie), and the death of Fonzie's father. Heck, I think they even brought back Fonzie's white blazer for one episode.

The Brady Bunch
Saved by the Bell
Newhart

I also recall the final season of Taxi being good. Carol Kane was promoted to regular and was featured more alongside Latka. The show was rolling.

Barney Miller
Taxi
Bob Newhart
Frasier
Cheers
Sienfeld

The King of Queens
Cheers
Growing Pains

I disagree about The Brady Bunch and Saved By the Bell (which don't meet the criteria for this list) and The Facts of Life and Newhart (which had bad final seasons).

The Jeffersons

The Facts Of Life

Who's The Boss

The Golden Girls

The Fresh Prince Of Bel Air

Alice

One Day At A Time

Happy Days

Laverne and Shirley

Gimme A Break

I also disagree about Brady Bunch. Just bringing in Oliver and one clunker episode (Kelly's Kids, a lousy backdoor pilot that probably should have been eliminated from syndication) doesn't ruin the whole season.

But back to the original question, going way back:

Father Know Best

The Adventures of Ozzie and Harriet

Everybody Loves Raymond

- Sisters (This night-time soap opera's sixth and final season, was reined back in - without going too over-the-top or maudlin the way the fifth season was. The storylines led perfectly to its impressive and moving two-hour series finale.)

- Knots Landing (For better or worse, this 14th and final season of this night-time soap opera was a good one.)

- Touched By An Angel (This drama series never stopped being good - right through its ninth and final season.)

- All In The Family. (I thought Stephanie was delightful. She was not annoying for me. I enjoyed the interactions among her, Archie, and Edith. It was also enjoyable to see Archie being tender and affectionate with both little Stephanie and his wife Edith - more so than in most of the previous season. Archie was also less proud and more humble, even though he remained fiery and headstrong at times. He had become an even more sympathetic character. All these factors made this sitcom's ninth and final season a good one.)

- The Jeffersons (This sitcom's 11th and final season was still a good season, even though the six remaining main regulars characters had been practically turned into caricatures - thanks to the writers [and maybe the directors and producers too].)

- The Golden Girls (All I can say is that I think this sitcom's seventh and final season was a good season.)

- The Nanny (This sitcom's sixth and final season was a good one. What more can I say about it?)

I agree about The Mary Tyler Moore Show. Great from start to finish. The Dick Van Dyke Show also had a good final season.

I thought season 5 (final season) of "That Girl" was really good.

I agree about The Mary Tyler Moore Show. Great from start to finish. The Dick Van Dyke Show also had a good final season.

Most shows start to go downhill after the early years. These two shows actually IMPROVED as they aged. Both ended at just the right point.

Gilligan's Island
Green Acres
Ozzie and Harriet
Brady Bunch
Leave It To Beaver
Mary Tyler Moore
The Odd Couple
Dick Van Dyke
Gomer Pyle
Family Affair
The Partridge Family
That Girl
Father Knows Best
I Love Lucy


These shows may have slowed down a little near the end but they were still consistently great from beginning to end and some of them even got better as they got older.

I wasn't going to add this because it only lasted 5 years but people are mentioning other shows that lasted 5 years. The Odd Couple was a good show in year 1 and a great show in years 2-5.

I didn't like the final season of Cheers because it didn't have Lilith as a regular for the full season. I am big Bebe fan, and sorely missed her presence. (Although the split worked so Frasier could have his spinoff)

I also thought Rebecca should have ended up with Robin.

The final TV season of the Red Green show was pretty good.

"Dr Quinn"
"The Nanny"