When Wendy sees the unconscious people strapped to machine, she exclaims "Holy Wachowski brothers!" in reference to the directors of The Matrix trilogy, which is about unconscious people connected to the Matrix virtual reality machinery.
Many references, including the code names Gatekeeper and Keymaster; Reitman University (Ivan Reitman directed "Ghostbusters"); the Egon Spengler Memorial award for Excellence in Physics; and Ray Parker, Jr Avenue (Ray Parker, Jr wrote the theme song for "Ghostbusters"). Also Stantz and Venkman, as well as mention of a 'PKE Meter'.
Louis wears a sweater with "COLLEGE" blazoned across the front, just like John 'Bluto' Blutarsky (John Belushi's character) in Animal House.
Entering the Omega Theta Nu party, Wendy quotes a line from "Star Wars": "You will never find a more wretched hive of scum and villainy."
The Middleman: "How in the eyeglasses of T. J. Eckleburg did you manage to break yours when we so desperately need confirmation?" T. J. Eckleburg is an oculist in The Great Gatsby by F. Scott Fitzgerald who left behind a faded billboard that pictures a large pair of blue eyes with half spectacles. The eyes look out over the "valley of ashes" and are thought to symbolize the eyes of God.
Ally: "Get your filthy frat boy paws off my unconscience sister."
Louis: "My pledge challenge was to boldly go where no man had gone before."
Tyler: "I can't even be friends with someone who likes the Zombies of Mora Tau."
Louis says "Great Caesar's Ghost", which is a phrase popularized in the 1950s television Superman series by Daily Planet editor Perry White.