Fans of "Psych," the quirky and clever USA dramedy about fake psychic Shawn Spencer, probably weren't surprised to learn that the series is airing its first-ever musical episode, "Psych: The Musical," on Dec. 15.

After all, Shawn (James Roday) and his BFF/detective partner Gus (Dulé Hill) are pop culture junkies, and the series has built entire episodes around Shawn's love of Tears for Fears, while equally pop culture-obsessed series creator Steve Franks wrote and performs the song's infectious theme song, "I Know You Know."

[Related: Best of Psych-os: 20 'Under Santa Barbara Skies' Video Reenactments in 30 Seconds]

Viewers, by the way, are in for a real holiday treat with the two-hour installment, which was written by the multitalented Franks; includes guest appearances by Barry Bostwick, Anthony Rapp, and Ally Sheedy; and revolves around musical theater in Santa Barbara.

And while a "Psych" musical ep makes perfect sense, the special installment got us thinking about past musical episodes of TV series that are not always, or ever, so musically inclined. We've rounded up a few of the weirdest, like the ones where Gilligan does "Hamlet," the prisoners of "Oz" get down with their bad selves and disco music, and "NCIS" boss Gibbs gets all "Guys and Dolls"-y in a hospital. Read on, and share your best/worst/weirdest musical TV episode picks in the comments.

1. "Gilligan's Island"

"The Producer" (original airdate: Oct. 3, 1966)

To prove to a creepy producer (guest star Phil Silvers) who has landed on the island that Ginger has real acting chops, Gilligan and company put on a musical version of "Hamlet" (with Gilligan, of course, in the title role). The plot works, sort of; the producer loves the musical so much that he leaves the island without the castaways so that he can take credit for the musical "Hamlet" he plans to produce. The episode, No. 52 on TV Guide's list of the 100 Greatest Episodes of All Time, is available on Amazon Prime and Amazon Instant Video.

2. "Buffy the Vampire Slayer"

"Once More, With Feeling" (original airdate: Nov. 6, 2001)

Weird, but fantastic: This Season 6 "Buffy" ep is a fan favorite for a reason. The musical sprang from the plot, in which a demon sparked Buffy and friends to randomly break into song to express hidden feelings that would ultimately change their relationships with each other. The episode — which was shown in interactive screenings in movie theaters, à la "The Rocky Horror Picture Show," after the "Buffy" series finale — is available on Netflix, Amazon Prime, and Amazon Instant Video.

3. "Scrubs"

"My Musical" (original airdate: Jan. 18, 2007)

A patient who hears everyone's speech as song leads to gems like "Guy Love," an ode to the bromance of doctors J.D. (Zach Braff) and Turk (Donald Faison), and "Everything Comes Down to Poo," a clever (and gross) song-and-dance number about stool samples. The Season 6 episode, which received five Emmy nods and won one for sound mixing, can be viewed on Netflix and Amazon Instant Video.

4. "Community"

"Regional Holiday Music" (original airdate: Dec. 8, 2011)

The original songs weren't classics, but that kinda fits in with the theme of the "Glee"-mocking ep, in which the study group is lured into joining the Greendale glee club by manipulative glee club leader Mr. Rad (guest star Taran Killam), who takes advantage of their personal issues. For Abed, it's about spending Christmas with his pals, which he does in the end. Speaking of the end, the closing credits, with Dean, Chang, Leonard, Magnitude, and Star-Burns, is truly gleeful. The episode is available on Amazon Instant Video.

5. "It's Always Sunny in Philadelphia"

"The Nightman Cometh" (original airdate: Nov. 20, 2008)

The Season 4 finale is, hands down, the FXX comedy's best episode ever, and it was such a hit with fans that the cast did a short tour in which they performed the ep live. In it, Charlie (Charlie Day) writes a catchy but very inappropriate musical that he hopes will persuade the Waitress (Day's real-life wife, Mary Elizabeth Ellis) to marry him. It all goes terribly wrong, of course, thanks largely to the gang's own narcissistic ways, but Charlie's yellow-tuxedo proposal is an example of the character's oddly endearing personality and Day's comic genius. The episode is available on Netflix and Amazon Instant Video.

6."Oz"

"Variety" (original airdate: Feb. 10, 2002)

It is truly bizarre, this Season 5 episode of the HBO prison drama that Entertainment Weekly tagged "Con Rock." The premise is that the prison is holding a variety show for the inmates, while the usual narration of Augustus Hill (Harold Perrineau) is also replaced with tunes. The highlight: a song-and-dance cover of the Barry Manilow/Lily Tomlin disco number "The Last Duet," performed by inmate Beecher (Lee Tergesen) and Schillinger (J.K. Simmons), the white supremacist who tortured him in unspeakable ways. The episode is available on Amazon Instant Video and HBO GO.

7. "That '70s Show"

"That '70s Musical" (original airdate: April 30, 2002)

In the show's 100th episode, Fez stars in the school musical and then imagines his friends in musical numbers with him. OK, maybe it's not so much weird as random, but also fun. No, wait, it is weird too, like the song-and-dance versions of "Happy Together" and "Shake Your Groove Thing," featuring the full participation of cranky dad Red Forman (Kurtwood Smith). The episode is available on Netflix and Amazon Instant Video.

8. "Grey's Anatomy"

"Song Beneath the Song" (original airdate: March 31, 2011)

When pregnant Callie Torres is injured in a car accident and in a semiconscious state, she hallucinates that she and her doctor pals who are treating her are singing, sometimes songs as literal as the Fray's "How to Save a Life." Groan if you will — and as even some fans of the show did at the episode, which is available on Netflix, Amazon Prime, and Amazon Instant Video.

9. "Fringe"

"Brown Betty" (original airdate: April 29, 2010)

"The Candy Man," sung by corpses? That's what happens when Dr. Walter (John Noble) smokes a strain of weed called Brown Betty, and hallucinates an episode that is part musical, part crime noir. No, really, that was some strong stuff old Walter got his hands on. The episode, which also includes Noble singing Tears for Fears' "Head Over Heels," was co-written by Oscar-winning screenwriter Akiva Goldsman and is available on Netflix, Amazon Prime, and Amazon Instant Video.

10. "Raising Hope"

"Burt Mitzvah: The Musical" (original airdate: March 28, 2013)

Burt's discovery that he's Jewish leads to a deli song about what it means to be "a member of the tribe," a song and dance at Howdy's about how to prepare a seder dinner, and an '80s-ish rock number in which Burt and Jimmy sing of how Burt is going to "rock the Torah" at his bar mitzvah. It's goofy fun, the songs are infectious, and it's another bit of proof that Garret Dillahunt, as Burt, is one of the most underrated TV comedy actors. The episode is available on Netflix and Amazon Instant Video.

11. "7th Heaven"

"Red Socks" (original airdate: Feb. 14, 2005)

Speaking of "Raising Hope," Emmy-nominated "Hope" star Martha Plimpton wrote this Season 9 episode of "Heaven," which found the Camden family getting all song-and-dancey on Valentine's Day. The highlight — if, as the song goes, you're acc-entuating the positive — includes Thomas Dekker, as Vincent, trying to cheer up a down-on-romance Ruthie by singing "Accentuate the Positive" and dancing with their school's baseball team. The episode is available on http://www.youtube.com/watch?v=YSnjAE2LQk0Amazon Prime and Amazon Instant Video.

12. "Batman: The Brave and the Bold"

"Mayhem of the Music Meister" (original airdate: Oct. 23, 2009)

Neil Patrick Harris is the titular baddie, the Music Meister, who uses music to compel superheroes like Black Canary, Green Arrow, and Aquaman to do his bidding. Batman eventually thwarts him with a sock to the jaw, but not before the 'toon terror's machinations lead to several tunes, including NPH expressing Meister's frustration with the Caped Crusader on "Drives Us Bats." The episode, which was nominated for an Emmy, is available on Netflix and Amazon Instant Video.

13. "Xena: Warrior Princess"

"The Bitter Suite" (original airdate: Feb. 2, 1998) and "Lyre, Lyre Hearts on Fire" (original airdate: Jan. 17, 1999)

"The Bitter Suite" was the show's first musical ep and featured mostly original tunes, but for pure weirdness and campiness, go with Season 5's "Lyre, Lyre," which featured Xena (Lucy Lawless) going to a battle of the bands and rocking covers of songs like "War," "(There's) Always Something There to Remind Me," and "Sisters Are Doin' It for Themselves." "The Bitter Suite" is available on Netflix, and "Lyre, Lyre Hearts on Fire" is available on DVD.

14. "Daria"

"Daria! The Musical" (original airdate: Feb. 17, 1999)

What sparked the musical numbers in this Season 3 episode of the "Beavis and Butt-head" spinoff? There's a storm coming, and that, apparently, made the town of Lawndale feel musical. Whatever, if you haven't seen it since it originally aired, or ever, be prepared to have papa Jake Morgendorffer's "Gah-gah-dammit!" stuck in your head for days. The episode is available on Amazon Prime and Amazon Instant Video.

15. "Chicago Hope"

"Brain Salad Surgery" (original airdate: Oct. 15, 1997)

You guessed it: brain aneurysm. Dr. Aaron Shutt (Adam Arkin) decides to leave Chicago Hope to teach at Harvard, then finds out he has a brain aneurysm that makes him hallucinate his fellow docs singing and dancing around him. Like a group version of "Luck Be a Lady," featuring a singing, dancing future "NCIS" star Mark Harmon. Dude, Gibbs would so not do that. Sadly, or not, the series is not available to stream, and the DVDs are out of print, so YouTube clips are all we have to prove that this musical event actually happened.

16. "Even Stevens"

"Influenza: The Musical" (original airdate: Jan. 25, 2002)

Ren gets the flu and her mom forces her to stay in bed, which bums Ren out because it will ruin her perfect attendance record. To cheer her up, Mom pops in a video of a musical, which leads Ren to imagine the school day in musical format. Fortunately, the entire ep is available on Disney's YouTube channel, which means you get to see a then-teen Shia LaBeouf — as Ren's bro Louis — croon and jam in the hallways about trying to scam his way out of a gym-class physical fitness test.

"Psych: The Musical" premiers Dec. 15 at 9 p.m. on USA Network.