Shawn says, "Gus, don't be the very model of a modern major-general."
In one of the songs Shawn says "don't Cheech my Chong"
Juliet asks Shawn, "Where are you?", and he replies, "The correct question is '*When* am I'?"
Gus meets Chris Lamberth and asks, "Like the Highlander?"
Gus refers to Paul Hogan as the "Crocodile Dundee guy."
Yang says, "He was the phantom," and Shawn responds, "Billy Zane!"
An asylum patient refers to Gus as "Hellboy."
Mentioned by Shawn Spencer: "It's like 'The Notebook'".
When Shawn and Gus are singing and dancing for Yang over Skype, the music playing is from the "Dazzle and Stretch" song Shawn made up when he gets a "vision" about an actress in "9 Lives".
Gus says that he is playing Burn-E in his Shakespeare in the Parking Lot tap show.
"Barry Bostwick" obliquely refers to his line (and song) "Dammit Janet" in the movie.