The following are what I've found, one way or another. Disclaimer: some references may have only been assumed.
- The (New) $25,000 Pyramid - multiple episodes
- Shelley Smith/Bill Cullen Day 4 (Animal Crackers)
- Adrienne Barbeau/Richard Kline Day 3? (You’re Not For Real)
- Press Your Luck - multiple episodes
- Super Password - 10/9/1984, 5/1/1985
- Trivia Trap - 10/23/84
- Sale of the Century (1980s syndicated version) - multiple episodes
- 2/22/85
- 10/??/85
- Sale of the Century (1980s NBC version)
- 8/11/88 (+ Heathcliff, both comic strip cats, 1st question)
- 11/22/88 (Speed Round question involving comic strip lasagna-loving cat; contestant incorrectly answered “Heathcliff”)
- Double Dare (Nickelodeon) - TBA (1986)
- Family Feud - 1988 (last episode w/ the Dainko family)
- Supermarket Sweep - multiple episodes
- 1992 (Garfield/Alpo question)
- 1994/95 (Garfield vitamins in Bonus Sweep)
- The Newlywed Game (GSN version) - 2011?
- Cash Cab - S4EP11, 2009
- Emogenius - Team Dancing Savages vs. Team Sailor Planet, 8/9/17
- America Says - S1Ep5, 6/22/18
- Generation Gap
- King of the Hill
- The Simpsons
- Family Guy
- American Dad!
- Robot Chicken
- MAD
- Futurama
- Batman: The Brave and the Bold
- Gravity Falls
- The Looney Tunes Show
- Home Improvement
- Just Shoot Me
- Charmed
- Married…With Children
- Wings
- The Nanny
- Full House (Opening (Seasons 1, 4, 5))
- Fuller House (Opening)
- Fresh Off the Boat
- Rick and Morty
- Pete Holmes
- Clarence
- Harvey Beaks
- The Loud House
- Amphibia
- Toon In with Me (apparently the episode "Four Dollar Bill", 11/29/21; "The Hoosier State", 5/23/24)
- Collector's Call (6/18/23 episode about the Kothes; 6/25/23 episode features Garfield shirt and Garfield wall clock; 9/8/24 episode)
- Svengoolie
- Short Circuit 2
- Air (2023 American film)
The following I've gotten from the Garfield website’s Cat-O-Vision (some of the above can apply here as well...especially if they were already listed):
- The Today Show
- Hour Magazine
- Late Night With David Letterman
- The Ted Knight Show
- World Series
- PM Magazine
- Good Morning America
- Showbiz Today
- Sunkist Fiesta Bowl Parade
- Murphy Brown
- Pat Sajak Show
- The Tonight Show with Jay Leno
- 41st Annual Emmy Awards Show
- A Current Affair
- Who’s the Boss
- Late Night with David Letterman
- Nightwatch
- Perfect Strangers
- Major Dad
- Entertainment Tonight (one episode with Waylon Jennings)
- CBS This Morning
- The Tonight Show Starring Johnny Carson
- Totally Hidden Video
- Late Show with David Letterman
- Anything But Love
- Family Feud
- Here & Now
- Hearts Afire
- Steals and Deals
- Joan Rivers Show
- America’s Funniest People
- Disney TV (“Happy Birthday, Garfield”)
- Dave’s World
- Wings
- The Nanny
- Caroline in the City
- The Naked Truth
- Married with Children
- Midday
- Wheel of Fortune
- Who Wants to Be A Millionaire
- Donny and Marie Osmond Show
- Saturday Night Live (Super Bowl Halftime Show)
- Dating Game
- On Air
- Extra
- Animal Icons