In Scream 6 (2023) a man in a Mojo Jojo costume passes the main characters. The voice actor for Mojo Jojo from The Powerpuff Girls also does the iconic Ghostface phone call voice.

In the original draft of Dawn of the Planet of the Apes (2014), Caesar's son was named River. The name was revised to Blue Eyes, but scenes still use the ASL sign for "River"

In Spider-Man ATSV (2023), there’s a really cool moment with a spider. Explanation in comments

Really awesome they showed this

Jorma Taccone voices the Vulture in Across The Spider-Verse, referencing a 2021 Miles Morales comic where he hosts SNL and does a skit with Jorma Taccone as the Vulture.

In Once Upon a Time in Hollywood (2019) Rick Dalton sings “Green Door” on Hullaballo. The song was referenced as a “portal to Hell” by late 60’s Manson-like cult leader David Berg. Rick Dalton also happens to have a green front door to his home.

In "Spider-man: Across the Spider-Verse" (2023), The Suit given by Stan Lee can be briefly seen during The Spider-men Chase Scene.

In Wolfwalkers (202, whilst Mebh is rummaging through Robyn's pockets, she casually tosses aside the 'Eye of Crom', an important item from Cartoon Saloon's first film, The Secret of Kells (2009)

Avengers Endgame (2019), Tony Stark has a mini-map on his HUD displaying the position on his allies. Later, when they discuss using the van, Tony marks its location with a red pin.

Neat little detail that I’ve never seen referenced.

In E.T. (1982) when Elliot first brings E.T. into the house the sign on Elliot's door reads "ENTER". When its shown again later a piece of paper has been added to the sign and it now reads "DO NOT ENTER".

In 2010 (1984) the American and Russian presidents on the cover of Time are Arthur C. Clarke and Stanley Kubrick, the author and director of 2001 : A Space Odyssey

Spider-Man: Across the Spider-Verse (2023): During Hobie's introduction, part of his Jamie Reid style punk-collage aesthetic uses a fictional article talking about an elusive vandal PLOMPS that defaced Big Ben, saying "It's not like they're Spider-Man" (Transcript of article in comments)