Wow! Coincidentally, I updated that Wiki page just a couple days ago with this new section.
In its 6 August 2015 issue, The New Yorker published a cartoon by Kaamran Hafeez that called back to the 87-year-old cartoon. A young girl and her mother are in a therapist’s office, with the caption, “You said, and I quote, ‘I say it’s spinach and I say the hell with it.’ Why don’t we start there?”
I can’t embed the image here, but you can see it here.
I wouldn’t call it famous, but this 1937 Paul Crum cartoon from Punch provided the name of a Doctor And The Medics album and was the inspiration for the name of Mike Nesmith’s autobiography .
I remember reading that when it released. I certainly didn’t think it fit in with the rest of the comic but I did feel the author took more than his fair share of heat for it.
“On Fire,” from KC Green’s Gunshow, features an orange dog with a hat sitting at a dinner table and drinking coffee.
One to watch that might not quite be there yet: I’ve seen this one from Zach Weinersmith’s Saturday Morning Breakfast Cereal a few times semi-recently on Twitter.
“The Curate’s Egg” (actual title: "True Humility’) is often referred to, especially in the UK. It is brought up in reviews of works that have both good and bad parts.
Yes, this one.
That and dickwolves.
Not a single strip because it’s the recurrence that makes it work, but Lucy, Charlie Brown and the football get referenced a lot.
Fearless Fosdick was Li’l Abner’s comic-within-a-comic by Al Capp. It’s a Dick Tracy parody that’s not so relevant today, but it did have enough of a cultural impact to get its own TV show and influence the creation of MAD magazine. While there’s no single strip that became iconic, the name “Fearless Fosdick” was recognizable as an over-the-top alpha male who blew everything to smithereens, regardless of the consequences.
Another classic xkcd:
And this:
Some historical ones have to be contenders:
About the Versailles treaty:
The iron curtain:
Napoleonic wars:
I’m missing something here. What does this mean?
Thank you—I too am stumped.
Another famous historical one: Dropping the Pilot:
How about Thomas Nast?
Santa Claus
Republican Elephant
Democrat Donkey
Oh and the cartoon that gave us the word Gerrymandering:
How many people have just added “iniquitous” to their vocabulary? 
Bull Moose Party
Years back, goofy video game comic Ctrl-Alt-Del tried to do a serious comic about having a miscarriage. It was not well received, and has since become a synonym for light entertainment trying to address a serious topic and failing badly.