Cole Sear (Haley Joel Osment) at the beginning of The Sixth Sense.
Coincidence? Two movies about ghosts and both have a character who wear glasses that don’t have lenses? Pretty sure that’s a very subtle easter egg.
Thomas Shanks, middle finger dean… Tommy Shanks, Mayor of Mellonville (John Candy, SCTV reference)?
In the original Ghostbusters when Louis Tully is trying to get into the fancy dining area and hes pulling on the doors and windows, they do the same thing with Erin when she’s trying to get to the Mayor/his assistant. Actually didnt realize 'till now lol.
The “books can’t fly” comment when Abby and Erin see each other for the first time could be a reference to the floating books in the library.
Come to think of it, “babies can’t fly” might mean GB2. Unless some babies can fly, of course.
Hey this film is quite quotable after all. “You found my pipe!”
I’ll tell you what, if I had a human baby that could fly I wouldn’t tell the press about it!
I’m assuming when Rowan turns into a cartoon it’s a nod to RGB.
It blew books off shelves from twenty feet away and scared the socks off some poor librarian!
Bust of Harold Ramis in the hallway when the Dean leaves Erin’s office in the beginning.
The original proton pack power-up sound was in the mix at one point!
The pack start up is there every time the new packs power on, it’s just mixed with other effects.
When Rowan is at work walking towards the camera in a hotel hallway, the apartment door behind him as Dana’s apartment number on it. Probably wouldn’t have noticed it if it weren’t for the imax 3D.
Damn that 3D was amazing.
Possibly wrong, but I think that Sigourney is wearing Egon’s jacket from GB1 when she turns up as Holtzmann’s mentor, which coupled with her ‘screw u’ brooch works as a nice mother and father of the character gag.
Then you’ve the ‘mass hysteria’ line too!
Awesome if true as it helps my theory she’s got part of Egon’s brain. 
During the big fight in Times Square, among all the bright and shining ads, is an ad for Twinkies… as if that wasn’t good enough, the slogan is “That’s a big Twinkie!” I totally flipped when I noticed it.
When we are introduced to Abbey and Holtzmann, the sign on their door reads “Do Not write STUPID things on this door!”
A Venkman Burn in Hell note reference. Also, Holtzmann’s pack readout after her amazing 30 second scene during the Times Square set piece reads 1984 (thank you Imax)
Also, Erin pulls the table cloth from the table upon her exit and the center item is still left standing ala Sedgwick “The flowers are still standing”
Fluted art deco facade of The Mercado is clearly inspire / a nod to 55 Central Park West
One of my favourites when Times Square transforms to the 70s, one of the cinemas lists a film “WELCOME TO THE OTHER SIDE” a possible nod to “See ya on the other side Ray” Can be located by keeping an eye out for the large Beyond the Fringe billboard on the street where Rowan gets the infamous crotch shot.