Many series have had Thanksgiving episodes, which I do not consider "specials." Still, I suppose I might as well at least list some of them, in passing. At least the ones I personally remember (even vaguely) seeing; surely there have been many I've seen that I've forgotten, and many more that I've never seen at all. I'm not going to be saying much of anything about the episodes here, so perhaps you'll find the links useful.

A-F

Gilmore Girls
Season 3: A Deep-Fried Korean Thanksgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia)
Season 6: He's Slippin' 'em Bread... Dig? (Amazon; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia)

Glee
Season 4: Thanksgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)

Heroes
Season 4: Thanksgiving (Amazon; A.V. Club; IMDb; Wikipedia)

How I Met Your Mother
Season 1: Belly Full of Turkey (Amazon; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)
Season 3: Slapsgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)
Season 5: Slapsgiving 2: Revenge of the Slap (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)
Season 6: Blitzgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)
Season 7: The Rebound Girl (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)

Life Unexpected
Season 2: Thanks Ungiven (Amazon; IMDb; Wikia)

The Michael J. Fox Show
Season 1: Thanksgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki)

The Middle
Season 4: Thanksgiving IV (Amazon; A.V. Club; IMDb; Wikia) There's a Thanksgiving ep every season, but I think this is the only one I've seen.

Modern Family
Season 3: Punkin Chunkin (Amazon; A.V. Club; IMDb; Wikia; Wikipedia)
Season 6: Three Turkeys (Amazon; A.V. Club; IMDb; Wikia; Wikipedia)
Season 8: Thanksgiving Jamboree (Amazon; A.V. Club; IMDb; Wikia; Wikipedia)
Season 9: Winner Winner Turkey Dinner (Amazon; A.V. Club; IMDb; Wikia)
Season 11: The Last Thanksgiving (Amazon; A.V. Club; IMDb; Wikia)

Murphy Brown
Season 4: Mission Control (IMDb; Wikia)
Season 11: Thanksgiving and Taking (Amazon; IMDb; Wikia)

My Adventures with Superman
Season 1: Hearts of the Fathers (Amazon; HBO Max; IMDb; TV Tropes; Wikia)

The Neighbors
Season 1: Thanksgiving Is for the Bird-Kersees (Amazon; IMDb; Wikia)
Season 2: Thanksgiving is No Schmuck Bait (Amazon; IMDb; Wikia)

New Girl
Season 1: Thanksgiving (Amazon; A.V. Club; IMDb; TV Tropes; Wikia)
Season 2: Parents (Amazon; A.V. Club; IMDb; Wikia)
Season 3: Thanksgiving III (Amazon; A.V. Club; IMDb; TV Tropes; Wikia)
Season 4: Thanksgiving IV (Amazon; A.V. Club; IMDb; TV Tropes; Wikia)
Season 6: Last Thanksgiving (Amazon; A.V. Club; IMDb; Wikia)

Northern Exposure
Season 4: Thanksgiving (IMDb; Wikia)

The O.C.
Season 1: The Homecoming (Amazon; IMDb; Thanksgiving Specials Wiki; Wikia)
Season 4: The Cold Turkey (Amazon; IMDb; Thanksgiving Specials Wiki; Wikia)

Parenthood
Season 2: Happy Thanksgiving (Amazon; A.V. Club; IMDb; NBC; Thanksgiving Specials Wiki)

Picket Fences
Season 1: Thanksgiving (Amazon; IMDb)

The Real O'Neals
Season 2: The Real Tradition (Amazon; IMDb; Wikia)

Scream Queens
Season 1: Thanksgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)

The Simpsons
Season 2: Bart vs. Thanksgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)

Single Parents
Season 2: Every Thursday Should Be Like This (Amazon; IMDb; Wikia)

Smallville
Season 10: Ambush (Amazon; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia)

Son of Zorn
Season 1: The Battle of Thanksgiving (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki)

South Park (There are other Thanksgiving eps, but these are what I remember.)
1997 short: Jay Leno Thanksgiving Special (Wikia)
Season 15: A History Channel Thanksgiving (Amazon; A.V. Club; IMDb; TV Tropes; Wikia; Wikipedia)

The Spectacular Spider-Man
Season 1: Nature vs. Nurture (Amazon; IMDb; MAU Wiki; Thanksgiving Specials Wiki; TV Tropes)

Speechless
Season 1: T-h-a-- Thanksgiving (Amazon; IMDb; Wikia)
Season 2: B-r-i-- British I-n-v-- Invasion (Amazon; IMDb; Wikia)
Season 3: C-e-- Celebrity S-u-- Suite (Amazon; IMDb; Wikia)

Sports Night
Season 1: Thespis (Amazon; A.V. Club; IMDb; TV Tropes; Wikia)

Stumptown
Season 1: November Surprise (Amazon; IMDb; Wikia)

Suburgatory
Season 1: Thanksgiving (Amazon; A.V. Club; IMDb; Wikia)
Season 2: The Wishbone (Amazon; A.V. Club; IMDb; Wikia)

Sunnyside
Season 1: Too Many Lumpies (Amazon; IMDb; Thanksgiving Specials Wiki; Wikia)

Supergirl
Season 1: Livewire (Amazon; A.V. Club; IMDb; Thanksgiving Specials Wiki; TV Tropes; Wikia; Wikipedia)

The Unicorn
Season 1: Turkeys and Traditions (CBS; IMDb; Wikia)

WKRP in Cincinnati
Season 1: Turkeys Away (Amazon; IMDb; Thanksgiving Specials Wiki)