Actor Allusion: In Season 1, Episode 11 "He Loves Me, He Loves Me Not, He Loves Me, Oops He's Dead" Shawn and crew end up speed dating and Shawn's first date is played by Teryl Rothery, who played the character of Dr. Janet Fraiser on Stargate SG-1. In the episode she says that she was raised on a farm and had a pet goat named "Cassy." "Cassy" is the name of the alien girl she adopted on SG-1 as Dr. Fraiser.
The Bourne references in "One, Maybe Two Ways Out" get funnier when you realize that Franka Potente, the spy in the episode, played Marie in the Bourne movies.
Shawn's forensic pathologist source (played by Kurt Fuller) tells him that a victim was killed by a Winchester 70. Fuller played Zachariah, an angelic enemy of the Winchester brothers on Supernatural.
In "Yang 3 in 2D," serial killer Mr. Yin is revealed to be a professor of fine art and history. The actor who plays him? Peter Weller, professor of fine art and history at Syracuse University. He really IS Buckaroo Banzai!
Kristy Swanson is suspected of being a vampire in "This Episode Sucks." This is particularly ironic when you realize what role Swanson is famous for.
Lucien (Tom Lenk) in the same episode had a recurring role in The Series.
And they run into a bartender played by Corey Feldman from The Lost Boys.
In "Shawn Saves Darth Vadar", Shawn tells an ambassador that he picked up his British accent from watching Phineas and Ferb's grandfather. The ambassador is played by Malcolm McDowell, who does the voice of Ferb's grandfather on Phineas and Ferb.
Really, it would be shorter to list the guest stars who don't get at least one of these jokes made about them.
Celebrity Paradox: Being big fans of Eighties pop culture, Shawn and Gus have made at least one reference to The Breakfast Club. But if Ally Sheedy played Allison Reynolds (you know, the basket case), then who's the serial killer Yang?
Judd Nelson, who has been personally referenced on previous episodes, guest starred in "Death is in the Air" as a scientist.
Then again, Judd Nelson looks very little like he did twenty years ago, so it doesn't seem so glaring when Shawn and Gus don't mention a resemblance.
Anthony Michael Hall was also in the film and was referenced before appearing in "No Trout About It" as Harris Trout.
Molly Ringwald also guest starred in "Shawn, Interrupted."
In the "The Head, the Tail, the Whole Damn Episode" in which Jeri Ryan guest starred, Shawn makes reference to the season finale of Leverage, where Ryan had been a semi-regular cast member in the same season.
They also like to reference movies Dule Hill appeared in: "Holes" in "65 Million Years Off" and "The Guardian" in "You Can't Handle this Episode". Thank God that The West Wing started in 1999 and really wouldn't be their sort of thing anyway, or else they'd be facing some very interesting paradoxes.
Defictionalization: The bad news is, Fries Queso Dos Fritos most likely don't exist. The good news is, fans have created recipes to replicate them!
Genius Bonus: Some of Shawn and Gus's references can be quite obscure.
In "Shawn (and Gus) of the Dead," Shawn realizes that Gus wasn't given credit for his help in finding the dinosaur skeleton on display at the museum. His response? "Oh man, Gus is gonna have an aneurysm when he finds out. And not thefunny kind, either."
In "Romeo and Juliet and Juliet" Shawn is fighting a martial artist(long story) and he tries to use the Crane Kick, along with the accompanying quote.
The whole episode "Dual Spires" is made of shout-outs to Twin Peaks. A brief list: It features the Log Lady (one of the strange themes and original Framing Device of Twin Peaks) a murder victim named Paula Merral (an anagram of "Laura Palmer", the young woman whose murder touched off Twin Peaks' story) who was known to run wild and was found wrapped in plastic next to a body of water. The opening theme is redone to sound like Twin Peaks'. The town is so small it appears on maps in parentheses. And then there's the final scene, which is nothing but Twin Peaks moments performed by Psych actors.
Far more directly, the guest stars are largely castmembers from Twin Peaks, including Dana Ashbrook (Bobby Briggs in the original, Bob Barker in the Psych episode), Sherilyn Fenn (Audrey Horne/Maudette Hornsby), Sheryl Lee (Laura Palmer/Dr. Gooden), and Lenny von Dohlen (Harold Smith/Sheriff Jackson).
Shawn himself can be taken as one big homage. Let's see: a smart mouthed guy named Spencer is too wild to be a cop but he's a great detective, so he and his Black Best Friend found a private detective agency where they take on cases that tend to become vastly more elaborate than they first seemed. I wonder where they got that idea.