Given Questionable Content's length and the artist's interests, lots:
Anime and Manga
- Negi and Nodoka show up in the third panel of #656.
- Several to Kiyohiko Azuma:
- Marigold has Yotsuba&! and Osaka posters in her room, and in "Magical Maidservant Mari-Chan", Marigold has a Sakaki-esque kawaii-gasm.
- You might miss the Azumanga Daioh shout-out here until you look at the title and watch the beginning of the show's opening. Even then, it's kind of subtle.
- Shelby the Great Pyrenees is drawn very similarly to Tadakichi-san.
- Marigold's hair in #1738 looks an awful lot like Chiyo-chan's.
- Marigold wearing a Haruhi Suzumiya sweatshirt and one of the people in line wearing a Death Note shirt.
- To Neon Genesis Evangelion when Dale pulls the Gendo pose. He's also a fan of Haruhi Suzumiya, going by the poster behind him.
- SAYONARA, SHELBY-SENSEI!
- The VespAvenger—a crazy girl on a Vespa who runs people down. Sounds familiar.
- Momo's original chassis is almost certainly a reference to Sumomo from Chobits.
- This comic appears to feature (third panel) a certain seven-year-old professor...
- Emily has an Imagine Spot where she pictures Tai's hair a variety of different colors and styles. One of those styles is Super Saiyan.
- When Faye tries on Marigold's glasses in this strip, Angus looks decidedly like Light Yagami from Death Note. Even the book he's reading now looks like a Death Note!
- In #2495, you can see a poster with Gally/Alita in the background.
- Beeps strikes a pose identical to one in the opening to Keep Your Hands Off Eizouken! complete with background pattern and color scheme. The page is even called Easy Breezy, the title of the theme song.
- Comic 1999 has an AnthroPC breaking out into song. Said song is a parody of the lyrics to the song of the movie of the same name: The Sound of Music.
- "Mawwage! Twue wuv!"
- Hannelore's dad in #2145:Drat, I was hoping I'd finally get to test out the paranormal containment unit I designed back in '84.
- In #1007, Pintsize alters the tagline from Alien ("In space, no one can hear you scream") to "In space, no one can hear you groan" (because pun).
- Faye can neither confirm or deny whether the line is a reference to Mission: Impossible Rogue Nation, which came out a week before the strip.
- There is one to Discworld. Hannelore mumbles part of Foul Ole Ron's catchphrase.
- Angus is reading a book by Jim Butcher.
- Ia, ia, Hannelore fhtagn.
Martin:I think today went pretty well. Mom seemed to like you
- I must not laugh. Laughter is the Marten-killer. Laughter is the little death that brings about total obliteration by an enraged Faye...
- After Martin's Mom, on the way out, gave Faye a final warning about how things were going to be.
Faye: Sheesh are you kidding? Today was like the test of the Mom Jabbar.
Martin:That was simultaneously one of the best Dune references and worst puns I have ever heard.
Accountant 1: She has the Voice!
- When Hanners storms into her mothers office and scares everyone else out with just a few words their reaction invokes the book, which Jeph lampshades in the comment for anyone who didnt get it. (DUNE JOKE)
Accountant 2: The Weirding Way!
- Hell, Jacques even works a reference to "The Cask of Amontillado" in #1123.
- The Hitchhiker's Guide to the Galaxy:
- "Script by Cassandra Clare". This was done in return for Clare writing in a QC reference in City of Lost Souls, in which she had Simon Lewis wear a "Clearly I Have Made Some Bad Decisions" T-shirt.
- This strip's title is a reference to Snow Crash's Raven.
- This strip has some fun lampshading how little a role Sven has played recently, with the Alt Text of "What was his name again? Svan? Svorn? Seivarden?"
- Marten Tiberius Reed. A Star Trek reference or maybe Stephen T. Colbert?
- Marten refers to Clinton as "Tom Servo" during one particular moment of creepiness.
- In the fifth panel of #2791, Claire models a certain ruffled dress from Firefly.
- Pintsize built some kind of computer that used Jack Bauer's login to access US nuclear missiles. Hannelore smashed it in time (Pintsize built it so Hannelore could save the world as a birthday present).
- Faye calling people "assbutt" may or may not be a reference to Castiel of Supernatural.
- Strip #1206 features Hannelore singing the Music/Battles song "Atlas".
- Strip #2112 is entitled Try Not To Rush.
- Claire models the infamous swan dress.
- Sven describes his personal music project as a "King Crimson meets Scott Joplin progressive ragtime masterpiece". Despite Dora's incredulous aversion to the whole idea, this may in fact be a Genius Bonus joke, as it's a fair description of King Crimson's song "Ladies of the Road"—suggesting that even when Sven tries to be original, he isn't.
- This page is one to Warcraft.
- A subtle reference to Metal Gear Solid in this strange lady's singing.
- A minor character by the name of Francis York appears.
- The mother from #3471 bears a resemblance to Sadayo Kawakami.
- Two Narbonic characters (Helen B. Narbon and Dave Davenport) appear in the first panel of #543.
- Kimiko Ross, Red Robot, and Eve make an appearance in #1421.
- #1391, covering eight different webcomics.
- Jeph's newspost for this comic says that it must be Depressing Comic Week at QC.
- There are several panels featuring Jeph's webcomic artist friends from the Northampton area walking by in the background.
- Davan and Nancy show up in this strip.
- There's a Red Robot, Geth and a Konata chassis for sale in #1998, which is even called "Robocameos". And the shop itself is called Idoru.
- A poster with a panel from this strip of Jerkcity is sometimes seen.
- A guest comic involving Deep-Immersion Gaming has Faye's rogue shouting "Sneak attack, bitch!"
- In this strip, discussing dinosaur anatomy summons Dina Saruyama .
- When May's battery runs out after she hooks up with Sven, and Sven looks up the internet to see what he can do about it, he notes that "there's an Er1-Ka Muon comic about it", a nod to Erika Moen's sexuality webcomic Oh Joy Sex Toy.
- Homestar Runner:
- Barry wears a "Dogs should be able to vote!" hat in #3248
- To Weebl & Bob (more specifically, Team Laser Explosion) in #382.
- Marigold has been shown wearing a "This Troper" T-shirt on Jeph's Tumblr.
- This is what happens when Jeph tries to get every anime/RPG reference out of his system at once.
- The "sympathetic party" who offers to help Bubbles recover her memories starting in 3391 is pretty clearly based on Anonymous. Their appearance is also very similar to Desire of The Endless or the cover art of Duran Duran's Rio album.
- When Melon and Yay Newfriend want to demonstrate to Roko their different ways of communicating with each other, Melon's speech bubble consists of the waveform of the old dial-up connection tone and Yay's speech bubble consists of the waveform of the white noise that ensued when you'd made a connection. Jeph's comment is "Only 90s kids will recognise this waveform."
- There's a Genius Bonus one in this one: when Faye snarks at Sam "Go finish your sprays, Gentileschi," it's a reference to 17th century Italian artist Artemisia Gentileschi, who became somewhat notorious for her amazingly gory pictures of the biblical story of Judith beheading Holofernes. Jeph references this.