Tatewaki is pretty much a shout-out to CDDrama!Setsuna. Except he's more of an unlucky butt monkey.
Episode 7 is a Sazae-san and a Fist of the North Star tribue. Ruby coming out of the pumpkin comically is reminiscent of the same scene in the Anime's Opening while Hattori himself is considered a Kenshiro Expy.
In episode 8, a background character is drawn similarly to Amuro Ray and when his girlfriend slaps him, he says "Not even my father hit me!"
Ruby is downing a costume similar to Marie Antoinette in episode 15.
In episode 7, after the prison explodes, the song "I Don't Want to Miss a Thing" by Aerosmith can be heard. The walk Kanon, Jill and Shouko do after getting out of the burning prison is reminiscent of Armageddon.
In episode 16-B, a timer appears on the bottom right of the screen, referencing 24. Also, the music that plays when Ruby and her friends are being chased by a boulder is a spoof of Indiana Jones's theme.
Towards the end of the same episode, a montage of Garnet working her many jobs, attending a dance audition and being approved by the judges is a clear spoof of Flashdance; her dance is an almost perfect recreation of Jennifer Beals' during the title song.
European dubs pulled one with the title of episode 30-A: "All The Teacher Iruka's Men"note the Japanese title is "Look Behind You", a reference to All The Presidents Men.
The M-Kage arc borrows very heavily from Batman, from M-Kage's costume to Nyangelina's role. The town it's set in is drawn in an obviously American comic book style.
In episode 33-A, Kanon "burns out" like in Joe's iconic death scene from Ashita no Joe.
Episode 34 is about the Plum class making a musical similar to West Side Story. Additionally, in one scene, Ruby and co. come out in French Revolution-style clothing, with Ruby looking like Oscar from Rose of Versailles. Jasper also comes out of nowhere dressed more-or-less like Spider-Man and shooting web out of his paws.
In episode 37, "Gonna Fly Now" plays when Ruby and Opal try to settle their dispute through boxing.
There's a bit of a Gintama shout out in the second half of episode 38. This is similar to the anime's 252nd episode and ended in the same way.
An in-series shout out occurs in episode 42 when Shouko's team, named "Sunshine", is next to a team named "Tinkle".
How both Garnet and Sapphie are defeated in episode 50 is nearly identical to how Kakyoin is killed in the Stardust Crusaders arc of JoJo's Bizarre Adventure.
During Labra and Master's battle scene in episode 50, Labra performs an attack similar to Kenshiro's "Hokuto Hyakuretsu Ken" from Fist of the North Star. The opening theme from the anime is played just to drive the reference home.
In episode 20, a parody of the Mission: Impossible theme plays when Blue Knight orders Garnet's guard force to attention. Garnet reveals that she has a beauty mask similar to Jason Voorhees'.
A parody of "Gonna Fly Now" plays in episode 22, when Ruby and Retsu are running around being Hot-Blooded.
In episode 24, Coal goes by the alias Coalupin in order to perpetrate a robbery.
In episode 25, there is an homage to Michael Jackson's "Thriller" video, featuring Ruby and the zombified sardines copying the dance moves. A bit from the song plays in the broadcast version, but not in the home video one.
In episode 35, Dian takes out his cards and says "Let's jewel". Might be just a subs joke.
In episode 39, Btooom!-stones; the subs-exclusive name given to the explosive stone that Ruby unknowingly threw at King's house.