I just watched The Conversation again, and the Flintstones was playing on the hotel room TV.

Another is The Shining where The Road Runner show was playing on the TV.

What other movies can you think of that have real shows playing on the TV?

I'm pretty sure the TV was playing some sort of kids show in Close Encounters of the Third Kind but I can't quite remember what it was.

Back to the Future also had the scene with The Honeymooners playing.

The Duff (2015) and One Hour Photo (2002) both have prominent scenes with The Simpsons. Though I'm not sure those count since they more or less actually draw from the episode (Mental state in One Hour Photo, the mom's entire subplot in The Duff)

There's probably quite a few.

21 Jump Street

Bill & Ted's Bogus Journey has the original Star Trek episode, "Arena" playing.

CHAPPiE had a scene with him watching He-Man and the Masters of the Universe. Only the opening credits/theme was shown though.

UHF-Beverly Hillbillies
Pulp Fiction-Clutch Cargo
Taxi Driver-American Bandstand
Crooklyn-Soul Train & Partridge Family
Scarface-T.J. Hooker
Born on the Fourth of July-Laugh In
True Romance-Santa Barbara
Stephen King's IT-Perfect Strangers
Love & Basketball-Family Matters
Pineapple Express-The Jeffersons
Mi Familia-I Love Lucy
Thunderheart-Mr. Magoo
Die Hard 2-Simpsons
187-Beetlejuice (Animated)
Action Jackson-Flintstones ("Yabbi Dabbi Doo!")

My Girl-All In The Family
Romy and Michele's High School Reunion-The Simpsons

I have to say that it takes me out of a movie/TV show when I realize the movie or show playing in the background belongs to the same studio/content owner. Same with Sony products in a Sony movie.

Also during the scene where Richard Dreyfus was assembling his very own Devil's Tower in the living room, the soap opera "As The World Turns" was interrupted by the special report of the train derailment. I thought the choice of show was a nice touch

I always like to note what's playing on TV in these scenes and it's usually movies and usually a clip to comment on the action, e.g. the scene from HE WALKED BY NIGHT (1949) with Richard Basehart shooting a cop used in MENACE II SOCIETY (1993). The only TV shows I remember used like this are the clips in TAXI DRIVER, "American Bandstand" already mentioned here, but also the soap opera clip when Bickle tips the TV over and busts it. The soap opera actors were credited in the end credits so I'm not sure if it was from an actual soap opera or an original scene filmed for the movie. Oh, and a clip from "Star Trek" featuring Nimoy used in TRANSFORMERS: DARK OF THE MOON, in which Nimoy participates as a voice actor.

We have done it before, and we will do it again. And, we will do it again.

The Professional featured Transformers.

Is it really in the background if the film makes a visible note of it playing? Like the He-Man bit in Chappie. It's not in the background. It's an active element for the film.

Anybody remember what Bill Murray (As a little kid) is watching in Scrooged?

Bullshit. Kevin Hart just really loved Vaio!

I sort of thought about that when I was posting it but overall it is just something randomly on when he turns on the tv. There's not a real storyline reason for it to be on.

Lone Ranger, I think.

^ Without looking, I'm wanting to say Howdy Doody.

In Blade II Scud is watching Powerpuff Girls cartoons.

I think so too. I seem to remember the Howdy Doody theme song kind of transitioning into the theme song for that giant dog show he was on as a young man. It's been a good ten years since I've seen Scrooged though.

In Grandma's Boy the grandmas were watching Antiques Roadshow.

I popped in the DVD. We were both right. Young Frank was flipping channels, starting off with Lone Ranger and landing on Howdy Doody when his dad comes in and tosses the veal at him.

Then Bill and Ted are pushed off the same cliff.