And in Margin Call, a stuffed lion toy shows up onscreen not long after Irons makes his first appearance.
A less subtle one from Disney: in Zootopia, Alan Tudyk voices a weasel named Duke Weaselton, who angrily corrects anyone who pronounces his last name “Weselton.” In Frozen, he’d voiced the Duke of Weselton, who has the same reaction to being called “Weaselton.”
I’m watching Dexter for the first time. I’m at the episode where Dexter’s sister calls Dexter’s new girlfriend “a gross English titty vampire”. Dexter replies that she has just described the perfect woman. His old girlfriend is an English vampire. (Whether she is gross or titty is up for debate.)
I don’t know if this is humorous, but I’m watching Kong:Skull Island, and Samuel Jackson, head of a helicopter team, is sending them off and he says “Like before, hold onto your butts.” He said “hold onto your butts” in Jurassic Park, when they were going to reboot the computer systerms.
From Weird: The Al Yankovic Story:
WEIRD AL: Are you saying you want to be my mentor?
DR. DEMENTO: No, I’m saying I want to be your…DE-mentor!
Which manages to be both a pun on “Demento” and a reference to the Dementors from the Harry Potter franchise, from which viewers might recognize the actor playing Weird Al.
It’s a good show. It’s a lot like Brooklyn 99, but with lower stakes and cute animals.
Rewatching Chuck. Girl comments to Chuck about someone being “ridiculously handsome”. Chuck dismissively says “Yeah, if you are into the strong Superman type of guy”. The girl was Lana Lang.
And the “Superman type” was Brandon Routh.
Rewatching old episodes of Felicity. A little complicated, but the title character Felicity has a crush on and is sort of friends with a guy who is lightly dating one of Felicity’s female friends. So, at a Halloween party Felicity sees the guy (who she is supposed to be there with, in matching costumes, except he doesn’t wear his) talking to a random woman dressed in a Pink Power Ranger outfit. Felicity and the guy get into an argument on a mostly unrelated subject, and she tells him that the next time he needs a friend to talk to at 2 AM, call the Pink Power Ranger. The aforementioned female friend of Felicity that the guy is lightly dating is played by Amy Joe Johnson, the actress who played the Pink Power Ranger in Mighty Morphing Power Rangers.
Not a “previous role” as such, but in a recently-seen episode of Law & Order: SVU a character refers to Olivia Benson as having "“An ass like the devil and a face like Jayne Mansfield”.
Benson is played by Mariska Hargitay, whose mother was…Jayne Mansfield.
In Meet the Parents, Ben Stiller’s character is asked to say grace at his fiancée’s parents’ house and jokingly responds “I’m not a rabbi!” Stiller played a rabbi in Keeping the Faith, which was released less than a year earlier.
Her dad, Mickey Hargitay, had a small role in an early episode, too.
In Vacation (2015), Rusty Griswold (Ed Helms) remembers the vacation he took as a kid.
National Lampoon’s Vacation (1983)
- James Griswold: I’ve never even heard of the original vacation.
- Rusty Griswold: Doesn’t matter. The new vacation will stand on its own.
Spoiler alert: it didn’t.
Late to the game, but there was an episode in The Middle where a character played by Ray Romano (who earlier starred in Everybody Loves Raymond) runs into the Heck family on a camping trip.
Patricia Heaton, of course, played Ray Barone’s wife Debra in Everybody Loves Raymond as well as Frankie Heck in The Middle.
IIRC at one point Ray Romano’s character tells Patricia Heaton’s character that she looks familiar and asks if they had ever met before. 
Woulda been better if they’d strongly implied the two slipped away from camp for a quickie.
IIRC, she was asleep in the back seat of the car that awful night.
It was reported (erroneously) that Jayne had been “decapitated” while she was “just” terribly mutilated. I’ve seen the post-crash photos, and they are horrendous.
Frand Drescher’s character in The Nanny actually ran into Fran Drescher’s character from This is Spinal Tap.
And Spinal Tap appeared in an early episode of The Simpsons, on which Harry Shearer (Derek Smalls) is part of the main cast.
It’s more of a current role, and it’s pretty explicit, but J K Simmons’ Farmers Insurance character comments on Santa in Red One.