Five-Man Band Concert

The Five-Man Band has been a long standing symbol of group unity, so what better way to do it than to show your cast actually performing in a band? It's sort of a cousin to the Dancing Theme, and shows the characters playing instruments, rocking out and having fun. Even if they never actually play the instruments in the series. If they do, though, all the better.

Compare to Fake Band. See also Duet Bonding.

Examples of Five-Man Band Concert include:

Anime and Manga

Seto no Hanayome OP, also a Dancing Theme.
Myself; Yourself OP.
In Marmalade Boy, Yuu and Kei, romantic rivals for the love of Miki, the female lead, are enlisted to help in a five-man band, along with Satoshi, the student council president, and two unnamed extras. All goes A-OK until Kei (who, by the way, is a piano prodigy) starts improvising just to show off. Luckily, the other members of the band react surprisingly well.
In one of the Suzumiya Haruhi drama CDs, Haruhi assigns the members of her Five-Man Band the exact instruments listed on the entry. This is despite them not knowing how to play these instruments. The five characters also appear dressed as rock stars on the cover art of one of the Image Song CDs and a poster for the Haruhi Suzumiya concert.
Shugo Chara's second ED depicts the Guardians as a band.
The premise behind The Prince of Tennis OAV named "Band of Princes"
Bubblegum Crisis: The Knight Sabers form a band in the video for 'Touchdown to Tomorrow.' They're also credited with a number of other songs associated with the franchise. Of the characters, Priss is the only one with a musical career.
The Slayers gang were pictures in official art as a band at least once, it also helps that the original cast sang their characters' songs for the soundtracks.
The Yu Yu Hakusho team was decked out in white tuxes for one of the concept albums. Both Toguros also make an appearance.
For an all-Meido Violin/Bass/Accordion/Drums band, Soredemo Machi wa Mawatteiru
K-On!, once they have five main characters. And the OP and ED sequences tend to be in music-video style, since we see them playing live during the shows.

Film

Film example: In the cult classic The Adventures of Buckaroo Banzai Across The 8th Dimension, Buckaroo Banzai and The Hong Kong Cavaliers are a literal Five-Man Band (prior to Buckaroo asking Dr. Sidney "New Jersey" Zweibel to join the group), and are featured in a scene where they give a concert at "Arnie's Artery". New Jersey joining the Cavaliers briefly makes them a Six Man Band, until Rawhide's death later returns them to being a Five-Man Band.

Live-Action TV

The Imagin Four-Temperament Ensemble of Kamen Rider Den-O has one of these where they sing the Do-It-Yourself Theme Tune. It is awesome. Supremely so.
On Superhuman Samurai Syber-Squad, while there were only four members, they were in a band.
In the Korean drama The First Shop of Coffee Prince, the Coffee Prince shop staff have a publicity concert that ends up being all percussion (but still awesome) because they really can't play instruments.

Western Animation

The Scooby Doo Gang would play concerts occasionally, Usually with Scooby on drums.
This was part of the premise of shows like Jabberjaw and Josie and the Pussy Cats, although the latter was more like a Power Trio Band Concert.
Several members of the cast of Code Lyoko form a band in an early Season 1 episode - Odd on guitar, Ulrich on keyboard, Jim on slide trombone, Nicolas on drums, and Yumi singing. Only Odd and Nicolas had any real skill at their instruments, and after that episode the band was never mentioned again.
All of Team Amazon does this for one song in Total Drama World Tour, with Heather as lead vocals, Courtney as the guitarist and Co dy as the bassist, but Gwen and Sierra switched, as the drummer and a squealing fangirl respectively. All of them have been shown singing because of the premise of the third season, but only Courtney has been shown playing her instrument outside of this song.