**Chester Goode ** Gunsmoke (1955-1964)
**Milhous Van Houten ** The Simpsons
Potsie Weber & Ralph Malph Happy Days
Carrie “I Hardly Ever Get Any Lines” Ingalls Little House on the Prairie
*Larry Dallas ** Three’s Company
The Cosby Kids * Fat Albert and the Cosby Kids
Lumpy Rutherford Leave it to Beaver
Mrs. Beasely Family Affair (special award of merit for being an inanimate object)
Rhoda Morganstern Mary Tyler Moore
Norm Peterson Cheers
Trapper John McIntyre MASH*
Rocket J. Squirrell The Bullwinkle Show (alternatively, Bullwinkle on Rocky and His Friends)
Buddy Sorrell and Sally Rogers The Dick Van Dyke Show
Gilligan Gilligan’s Island - Maybe the only show where the sidekick was the star
And in the real world…
Ed McMahon The Tonight Show
Paul Shaffer The Late Show with David Letterman
Willard Scott The Today Show
And maybe the best TV sidekick of all time…Mariette Hartley to James Garner in a series of Polaroid camera commercials
I have to second, third, whatever Barney Fife. Don Knotts was amazing in that role, because by playing it as straight as he did, it made the character hilarious.
Other great sidekicks:
TV’s Frank from MST3K
Butters from South Park
No, but you reminded me of another one; Angel Martin on The Rockford Files.
Dog Columbo
Surprised that Festus of Gunsmoke hasn’t gotten a nomination yet.
Tied for first in my mind are Barney Fife and Ed Norton.
I was stunned to see the thread went to post #14 before anyone mentioned Barney Fife!
Dipping into the 1960s era cartoons we have:
Baba Louie to Quick Draw McGraw
(“I don’t thin that’s a good idea, Quix-draw.”)
and
Boo Boo Bear to Yogi Bear.
Of course, Huckleberry Hound didn’t need any sidekick. 
People, people people! How could you forget Barney Rubble?
Yeah. Especially when she kicks really high. Rowr!
Chickotay (ST: Voyager)
Howard Borden, Jerry Robinson (The Bob Newhart Show)
George Michael (Arrested Development)
Skippy (Family Ties)
Artemis Gordon.
Odio Coloney on the King Leonardo cartoons.
Itchy brother. Biggie Rat’s sidekick on the same show.
Socrates Poole - “The Adventures of Brisco County Jr.”
The Robot from Lost In Space.
Ernest Penfold from “Dangermouse.”
More votes for Ed Norton, Barney Fife, and Barney Rubble.
Probably one of the first in television
Patrick Alouious Brady to Roy Rogers (you remember Pat he drove Nelliebelle)
Range Rider had Little Beaver (played by Robert Blake by the way)
Has anyone mentioned Mindy of Mork and …
Paul Drake for Perry Mason
Andamo for Mr. Lucky
The Burt Reynolds character in Riverboat
The oriental guy in Quincy
Higgins in Magnum PI
1928 Porter/Mom: “My Mother the Car”, Ann Sothern (as the car) played the sidekick role to Jerry Van Dyke (or was it the other way around?)
Jingles (Andy Devine) - The Adventures of Wild Bill Hickock
Hey, Wild Bill, wait for meeeee!
Mr. Greenjeans to Captain Kangaroo
Wally from the comic strip Dilbert
Snowman from Smokey and the Bandit
Linus From Peanuts