Barry Bostwick
Barry Bostwick, of Spin City and Rocky Horror Picture Show, showed up in 2013's Psych: The Musical as Roland Armitage, the womanizing owner of a Santa Barbara Theater, and he apparently had a blast. "They are doing the hardest job possible, being funny and smart for 14 hours a day," he told E! News of working on the show. "The most inviting and enthusiastic cast and crew. Totally appreciating what they have and they keep polishing the gem. Who knew they could sing and dance, the whole world does now. Nothing but a joyous and positive experience. They even snuck in a Dammit Janet joke!!!!"
Rachael Leigh Cook
The She's All That star played Shawn's high school crush and later girlfriend, Abigail Lytar, in six episodes of seasons four and five.
There was literally nothing wrong with the character of Abigail Lytar, except that she was not Juliet, and when Shawn opted for saving Abigail over Jules in the season four finale, our hearts were temporarily broken.
Freddie Prinze Jr.
The other star of the seminal 1999 teen rom-com She's All That showed up on Psych to play Gus and Shawn's nerdy friend Dennis in the one and only time we've ever heard of this so-called friend—the season five episode, "Not Even Close...Encounters."
As a child, he was an expert on UFO's and other such nerdery. As an adult, he's hot and athletic with an equally hot wife, and has a secret room in which he keeps his shrine to all the best sci-fi that has ever lived, including LaVar Burton's glasses from Star Trek and Colonel Adam's helmet from Battlestar Galactica. It was a nerdy '90s girl/guy's dream come true and it was beautiful.
Valorie Curry
The Following star helped bring the creepy to the already creeptastic season six episode, "Heeeeere's Lassie," playing a pregnant woman named Rosemary, because of course.
Tony Hale
The Arrested Development star appeared in the season six episode "Neil Simon's Lover's Retreat" as businessman, wine enthusiast and murderer Jerry Kincaid, along with other guest stars Jason Priestley and Arden Myrin. Apparently, it's not hard to keep Hale happy on a job like Psych: "The lead actors took us all out for sushi the first night I was there. I was immediately sold," the Veep star shared.
Corbin Bleu
The High School Musical star popped into fake Santa Barbara for the season eight episode, "Shawn and Gus Truck Things Up" as Luther/Smokey, a musical theater major who scams food trucks by robbing them and then coming back later to get them to pay protection money. It was a pretty genius scam until Shawn, Gus and Luther's mother caught up with him.
Martin Mull, Lesley Ann Warren, Christopher Lloyd
The "100 Clues" episode in season seven was not only the one hundreth episode, but was also the episode that was entirely an homage to the 1985 whodunnit movie Clue. It also featured three of the stars of that movie—Martin Mull, Lesley Ann Warren and Christopher Lloyd—and several stars not of the movie, like Curt Smith and Garrett Morris. It was a veritable treasure chest of references and strange nostalgia and it was wonderful.
Corey Feldman
Feldman, famous for such iconic '80s films as Stand By Me, The Goonies, Gremlins and The Lost Boys, took a little trip to Santa Barbara for, what else, the vampire episode. In season six's "This Episode Sucks," Feldman played a bartender working in a vampire bar, which is apparently a thing that does exist outside of Bon Temps, Louisiana. The episode also marked the debut of Kristy Swanson, the original Buffy, as Lassiter's criminal girlfriend Marlowe.
Mira Sorvino
Mira Sorvino—also known as Romy, to fans of Romy and Michele's High School Reunion—joined the Psych gang for just the last three episodes of the series. Like Lassiter, we were at first not sure about her sunny disposition or the fact that her name is "Betsy." However, she quickly proved herself worthy of her title of lead detective and we're fairly sure Santa Barbara is in safe hands.
George Takei
Takei appeared in the season one episode, "Shawn Vs. The Red Phantom," and played a rather high-maintenance version of himself, while Shawn and Gus posed as his assistants. He even closed out his appearance by storming off in a huff after being upstaged by Shawn at the comic book convention, and it was a pretty awesome treat for fans of Star Trek, cartoons, comic books and just things in general.
Peggy Lipton
The Mod Squad actress played the present-day version of Scarlett Jones, the girlfriend of infamous Santa Barbara mobster Rodney Caruso, in the season eight episode "1967: A Psych Odyssey." She said of the experience: "My scene with Tim was silly and fun! He has the dash and sense of humor of Jimmy Stewart plus tall and handsome too! A great afternoon spent in the Interrogation room!"
Jason Priestley
The leading man of Beverly Hills, 90210 may have played a con man when he showed up on Psych in season six's "Neil Simon's Lover's Retreat," but it didn't make us love him any less—especially when he turned out not to be the murderer.
Josh Malina
You may know him as Scandal's David Rosen, or even as The West Wing's Will Bailey, or from one of his many other roles over the years. But for one glorious hour in season four's "Let's Get Hairy," he was Stewart Gimbley and he believed he was a werewolf. He even wore a diaper and a wolf cape, and it doesn't get much more gleefully ridiculous than that.
Christine Baranski
Before she was Diane Lockhart on CBS's The Good Wife, she was Alice Clayton, wife of a murdered billionaire, who was having an affair with her tennis coach. How scandalous! It was the perfect Christine Baranski role—classy, refined, and yet just a little bit ridiculous.
Kenan Thompson
First, he was a comedy genius on Nickelodeon's All That and Kenan & Kel, and then he joined the SNL cast in 2003. In 2009, he took a break to guest star, along with Jaleel White, in the season four episode "High Top Fade Out," as Gus' estranged college buddy. He also got to show off his singing skills as a member of Gus' college acapella group, Blackapella, and we'd like their rendition of "Swing Low, Sweet Chariot" as a lullaby and/or ringtone please.
Molly Ringwald
The leading lady of the Brat Pack (and the third of the four Breakfast Club cast members to guest star) completely freaked us out as the strict head nurse McElroy at the mental hospital where Shawn goes undercover in the season six episode, "Shawn, Interrupted." Despite her slightly murdery vibe, she was only guilty of messing with a patient's medicine dosage in order to help the murderer get away with the murder.
Jaleel White
Who knew Family Matters' Urkel could sing?! Jaleel White, of "Did I do that?" fame, played Tony—a member of Gus' college acapella group, Blackapella—in two episodes in seasons four and six. His voice, combined with the sounds of Dule Hill and Kenan Thompson ("High Top Fade Out") or Mekhi Phifer ("Let's Doo-Wop It Again") and sometimes even James Roday, could put us to sleep in the best way.
William Shatner
William Shatner played Juliet's charming criminal of a father, Frank O'Hara, in two season six episodes, "In For A Penny," and "Heeeeere's Lassie." Of working on the show, the Star Trek icon said, "I had the best time working with the cast, director and production people of Psych." He also couldn't resist throwing in a little home country pride: "They're a credit to Canadian production."
Jeffrey Tambor
The Arrested Development patriarch played Juliet's step-father Lloyd in the season seven episode, "No Country for Two Old Men." As it turned out, he wasn't much of a step up from Juliet's actual con-man father (played by Shatner). His gambling debt ends up sending both Lloyd and Henry to Mexico, where they participate in shoot-outs, almost get arrested, and are forced to dig their own graves.
Nestor Carbonell
Nestor Carbonell of Lost (and eyeliner) fame played Declan Rand, a rich, famous, and successful version of Shawn who used his own fake psychic skills as a criminal profiler. He was also the worst, because he managed to woo Juliet. However, his appearance in two episodes of season five—"Shawn 2.0" and "One, Maybe Two Ways Out"—gave Shawn the little boost of urgency he needed to finally express his feelings to Jules and the rest is Psych history.
Anthony Michael Hall
This Breakfast Club star was one we could probably have done without (or with a different role), as his character was not a very welcome addition to the group. Chief Vick was suspended, Lassiter was demoted and Psych was fired (along with poor Buzz McNab) when Hall's Harris Trout took over the SBPD in season eight. He didn't last long, though, and Lassiter was then finally promoted to Chief of Police.
Jane Lynch
Before she rocked the track suits on Glee, she was Chief Vick's Coast Guard commander sister, Barbara Dunlap, in the season three episode, "There Might Be Blood." "There's something really special about shooting in Vancouver," Lynch said of the experience. "There's a laid-back quality that is so liberating for creative types. And it was full blown for the fabulously funny cast of Psych. I also loved the contrast of pretending to be in sunny Santa Barbara whilst it poured rain in Vancouver."
Ally Sheedy
Ally Sheedy was the first of four Breakfast Club stars to appear on the show and her role was a doozy. Her first episode, "An Evening with Mr. Yang," revealed her to be Mr. Yang, the serial killer whose obsession with Shawn left a deadly impact on various people in his life, from the girl who served him breakfast to his mother, Madeleine (Cybill Shepherd). Luckily, Shawn was able to save his mother, and Yang was arrested. However, she returned for three more episodes, including two more in the Yin/Yang saga, and 2013's Psych: The Musical, in which she died from a stab wound. RIP, Mr. Yang. You and your fun-loving serial killer-y ways will be strangely missed.
Cybill Shepherd
The star of Moonlighting and Cybill first showed up as Shawn's mom Madeleine in the season three premiere, "Ghosts." She appeared in four more episodes, including one where she was held hostage (and strapped to a popcorn bomb!) by the serial killer Mr. Yang (Sheedy). After the season seven episode, "Juliet Takes A Luvvah," Madeleine never appeared again, perhaps because Shawn was scarred for life after walking in on Madeleine and Henry rekindling a bit of their former love.