On Frasier, Laurie Metcalf as a frustrated “Nanny G” asks the titular character if he has “any idea what it’s like to play the same character for 20 years,” an allusion to Kelsey Grammar’s role on Cheers!
On The Beverly Hillbillies, Bank President Milburn Drysdale mistakenly addresses actor “Dash Riprock,” played by Larry Pennel, as “Ripcord.” Ripcord was a syndicated TV series of the early '60s, in which Pennel played skydiver “Ted McKeever.”
Can you think of any others?
Nathon Fillian droped a few references to his prior work on Firefly, mostly just one liners, but the most notable one being where he dressed in his Malcom Reynolds outfit for Halloween.
In the Crazy Ones, Sarah Michelle Geller dropped an allusion to Buffy at one point. Though that may have been an outtake shown with the credits at the end.
My favorite of those is when Castle and Beckett are pursing a suspect, and encounter a couple of Chinese workers. They don’t understand Beckett asking them a question in English, but after Castle says something to them in Chinese, we get this exchange:
Beckett: “Semester abroad?”
Castle: “No, a TV show I used to love.”
The joke requires one to know that, in the Firefly universe, both English and Chinese were widely spoken, and all of the characters regularly dropped Chinese expressions into their dialogue.
Probably not quite what the OP is after but Peter Capaldi appears in the credits of World War Z as “W.H.O. Doctor”, his last role before playing the Doctor.
In the movie Stakeout, the two leads are playing a game in which one gives a random line and the other guesses the movie that it’s from.
Emilio Estevez: “This was not a boating accident!”
Richard Dreyfuss looks up for a second and then quickly says, “I don’t know.”
The line of course was actually spoken by Dreyfuss in Jaws.
It seems this really happened on the set between the two actors and they decided to work it into film.
That’s a good one! 
I’ve been re-watching “30 Rock” and they have lots of references like this.
Alec Baldwin’s character says “I once called myself God in a deposition.”
Alex Baldwin’s character also says “Do TV and no one will ever take you seriously again. It doesn’t matter how big a movie star you are, even if you had the kind of career where you walked away from a blockbuster franchise or worked with Meryl Streep or Anthony Hopkins, made important movies about things like civil rights or Pearl Harbor, stole films with supporting roles and then turned around and blew them away on Broadway. None of that will matter once you do television.”
Alan Alda guest stars in an episode and says “What’s all this crying about babies and chickens? I thought this was supposed to be a comedy show.”
In The A-Team, the team visited Universal Studios. Dirk Benedict’s character sees a Cylon, and does a double-take.
In the film version of Maverick, Mel Gibson’s character encounters a character played by Danny Glover, and they both do a double-take.
I just remembered this exchange between William Shatner and John Lithglow on Third Rock from the Sun:
In the Monk episode “Mr. Monk and the Airplane”, Sharona spots Tim Daly on their flight, leading to this exchange (paraphrased):
Monk: “Is he some sort of actor or something?”
Sharona: “He was on that show Wings.”
Monk: “Never saw it.”
Tony Shalhoub of course was on Wings, too.
from N.C.I.S.
“What did Ducky look like when he was young?”
“He looked like Ilya Kuryakin.”
In the failed but fondly remembered John Larroquette Show, co-star Alison LaPlaca came up with this:
Joe Pesci’s commercial for SBC Internet Services
Did you know today is her birthday?
(I didn’t. I just wanted to look her up.)
It’s also Beethoven’s birthday, BTW. Happy Beethoven’s Birthday!
In this scene from Boston Legal, James Spader refers to “sea lice” as “cling-ons”. Willam Shatner playing Denny Crane replies “Did you say Klingons?”
In What’s Up Doc?
Barbra Streisand: Let me tell you —love means never having to say you’re sorry."
Ryan O’Neill: That’s the dumbest thing I’ve ever heard
Which, of course, alludes to Ryan O’Neill’s famous scene from Love Story
How about Ryan Reynolds call back to both Green Lantern and X-Men Origins in End Credits scenes of Deadpool 2.
In Paul, as Sigourney Weaver’s character is about to attack Kristin Wiig, Blythe Danner’s character decks Sigourney saying the iconic “Get away from her you bitch !!!”
In Sex and the Single Girl (1964), Tony Curtis’s character is often mistaken for actor Jack Lemmon, prompting this exchange with Natalie Wood’s:
Helen Gurley Brown: I hope you don’t feel odd or anything because you’re wearing a woman’s robe.
Bob Weston: Oh, no! Not at all! In fact, I was thinking I look just like - eh - Jack Lemmon did in that movie where he dressed up like a girl. Remember?
An allusion to Some Like It Hot (1959), which starred Curtis, Lemmon, and (of course) Marilyn Monroe.